SIGNALLING AND THE DESIGN
OF THE GASK RIDGE SYSTEM
D. J. Woolliscroft
University of Manchester


Gask home Abstract

This paper attempts to describe the signalling arrangements of the Gask Ridge and the influence these may have had on the general layout of the system, in an effort to understand the purpose and context of the Roman line It also reports on the re-excavation of a possible Roman fortlet within metres of the Gask Ridge tower of Midgate (NO 02112047). This juxtaposition suggests that the Gask Ridge fortlets may not be exactly contemporary with the towers. But, although, for the moment, there is insufficient evidence to prove whether they belong to another Flavian phase, or to a different period altogether, the former may still appear more likely.

Background

Scientific study of the Gask Ridge began at the turn of the century with the excavation by D.J. Christison (Christison, 1901, 15-43) of the fortlet of Kaims Castle and some of the eight watch towers then known on the Ridge itself. But, although a great deal was learned through this programme, none of the sites yielded dating evidence and, as we shall see, the excavation of the fortlet may have been flawed. Since then another fortlet has come to light at Glenbank (Maxwell, 1990, 354-9), to the south of Ardoch, along with evidence for ten new towers, bringing the number known or suspected (1) to 18 (fig 1). The towers can also now be seen to fall into two distinct groups, although the significance of the change is uncertain. For, whilst those to the north of Kaims Castle, including those on the Gask Ridge itself, have a single surrounding ring ditch, those further south have two. Furthermore, a single stratified Flavian sherd from Gask House (Robertson, 1974, 20) and a possible second from Westerton (Private communication), both in the northern group, have finally provided a probable date for, at least, the single ditched towers, whilst the discovery of the Flavian fort at Doune has suggested a possible destination for the southern end of the system (Maxwell, 1984, 217-24).

A picture has, thus, been built up of an integrated Flavian system, stretching (at least) from the Teith at Doune to Bertha on the Tay and the fortlets of Glenbank and Kaims Castle have usually been seen as part of this system, despite their current total lack of dating evidence(2). With this much apparently settled, the debate has moved on to consider the exact context in which the system was built. For example, some scholars would argue for an early date, with the line forming part of the provisions made during Agricola's 4th season (Hobley, 1989, 73-4) and later replaced by the glen-blocking forts. Others support a later date with the system representing an attempt to hold a frontier line defending Fife in the aftermath of the abandonment of Inchtuthil and the rest of northern Scotland (Breeze, 1982, 61-65).

Cases can also be made for regarding the Gask as a "back stop" frontier, for which the glen-blocking forts served as outposts, or for seeing the glen-blockers as the true frontier with the Gask as merely a closely watched road supervising the strategic invasion route through Strathearn (Pitts and St Joseph, 1985, 278). Yet, despite the fact that three of the four forts on the system, Ardoch (Breeze, 1983, 224-43), Strageath (Frere and Wilkes, 1989) and Bertha (Adamson and Gallagher, 1986, 195-204), have Antonine as well as Flavian occupations, the assumption that all the more minor installations belong to a single Flavian line has persisted throughout these discussions.

If this was the case, we would appear to have a fairly logically laid out system. The presence of Glenbank between Doune and Ardoch, and Kaims between Ardoch and Strageath suggests an alternating series of forts and fortlets set out along the road and interspersed with a closely spaced series of watch towers. Attempts to find signs of a regular tower spacing interval, based on the Roman mile (Rivet, 1964, 196-8), have never proved wholly convincing , but this need hardly surprise us in view of the irregular tower spacings on the contemporary Wetterau Limes, to the north of Frankfurt in Germany (Woolliscroft and Hoffmann, 1991, 531-543).


TABLE ONE: GASK RIDGE SITE SPACINGS

Glenbank - Greenloaning c2,300m

Greenloaning - Ardoch c2,750m

Ardoch - Blackhill Wood 900m

Blackhill Wood - Shielhill South 875m

Shielhill South - Shielhill North 950m

Shielhill North - Kaims Castle 875m

Kaims Castle - Westerton 2,300m

Westerton - Strageath c4,200m

Strageath - Parkneuk 1,750m

Parkneuk - Raith 1,520m

Raith - Ardunie 1,510m

Ardunie - Roundlaw 1,110m

Roundlaw - Kirkhill 960m

Kirkhill - Muir o' Faul. 1,440m

Muir o' Fauld - Gask House 870m

Gask House - Witch Knowe 800m

Witch Knowe - Moss Side 1,120m

Miss Side - Midgate 1,400m

Midgate - Westmuir c915m

Westmuir - Peel c3,975m

Peel - Huntingtower c1,940m

Huntingtower - Bertha c3,175m


It is, however, apparent that the system as we have it today cannot be complete. Glenbank is not intervisible with Doune and, although Huntingtower would, from its likely original tower height, have been visible from Bertha, both spacing and signalling considerations suggest that further towers await discovery at both ends of the line. Other obvious gaps exist between Westmuir and Peel, Westerton and Strageath and Greenloaning and Ardoch, whilst a number of smaller gaps (Table One) might also repay attention.

At one time it also seemed likely that the system continued south, beyond Doune, perhaps to the Flavian fort of Camelon. For a well preserved hill top ring ditch at West Plean, to the south of Stirling, was once interpreted as a tower of the Gask Ridge type (Crawford, 1949, 18). This has been shown to be non Roman (Steer, 1956, 227-51)(3), however, and all that can now be said is that, whilst extensions to the south of Doune or, indeed, to the north of Bertha cannot be ruled out, there is no firm evidence that they existed.

The signalling system

Despite these gaps in our knowledge it is possible to reconstruct at least a skeletal signalling system for the Gask Ridge, as currently understood, based on a study of each installation's field of view, from its likely full original height (Woolliscroft, 1989b, 5-19). For, as all long range Roman signalling relied on visual techniques (Leiner, 1982), direct communications could only take place between intervisible sites. The reader is cautioned from the outset, however, that such a study can only show what was possible or, at best, likely. For, signalling is a process that leaves little physical trace and attracted scant detailed comment from ancient writers. It must always be remembered, therefore, that the fact that a signalling system was apparently both possible and desirable on a given Roman deployment does not necessarily mean that any such system actually existed. That said, there are design oddities on a number of Roman frontiers that only seem to make sense as moves to accommodate signalling (Woolliscroft 1989a and Woolliscroft and Hoffmann 1991) so that some signals provision does appear likely on many, if not all, of Rome's major military systems.

In fact, almost all of the known Gask Ridge installations are intervisible with both of their immediate neighbours and in the few cases where they are not, (Westmuir, for instance, cannot be seen from Peel) it already seems likely on spacing grounds that the sites are not true neighbours, as intermediate towers may still remain to be found. It should, therefore, have been possible to pass signals from tower to tower along, at least most of the line. Indeed, mutual intervisibility between neighbours seems to have been regarded as important and, as on the Wetterau Limes in Germany, there are signs that the irregular inter-site spacings are, to some extent, caused by the need to ensure it. For example, there is a tendency, especially on the Gask Ridge itself, for the towers to be sited on or near pronounced changes in the angle of slope of the ground, so that a number of sites are set at the limit of the field of view of one or other of their neighbours and so appear on their sky line. Where this is the case on the Ridge itself, it is usually a site's eastern neighbour that marks the limit of its vision, which suggests that the system may have been laid out from the west. Indeed, so pronounced is this tendency, that it becomes easy for a first time visitor to locate the sites on the ground with little help from a map. Nevertheless, as the inter-site spacings are generally quite short (if slightly longer than those in the Wetterau), ranging from c800m to just over 1,500m (Table One) and many of the installations have fairly extensive views, most can see sites well beyond their immediate neighbours, at least in one direction. There are, thus, considerably more sites than would have been required for a simple line of relay stations. For in such a system each installation might be expected to lie at or near the limit of view of both its neighbours so as to use the longest possibly links and the smallest number of stations. This apparent over provision may require explanation and this, in turn, may have implications for signalling. So before attempting to interpret the intervisibility data from the sites, it is worth taking a closer look at the likely role of the system.

Donaldson (1988, 352-3) has argued that the fact that the Gask Ridge sites are so closely spaced suggests that the signalling techniques employed on the system were limited in range to around a Roman mile. But experiments by the writer (Woolliscroft, 1993, 26-61) have shown that almost all the recorded Roman visual methods were capable of much greater ranges, even in less than perfect weather: especially the relatively primitive, beacon based, alarm signals that are likely to have been of most use on the frontiers (Woolliscroft, 1989a, 9). This means that although the Gask may have had a signalling system, it cannot be thought of as only being a signalling system. Furthermore, whilst it would certainly have been possible for the line to have operated in a strictly linear manner, with signals being relayed from site to site through every link in the tower chain, this would have been both unnecessary and inefficient (Woolliscroft and Hoffmann, 1991, 534). It would also have been slow, for a signalling system based on relays only a few hundred meters apart is likely to have been little faster than a mounted messenger, even if it was only intended to carry simple alert beacons. If it was expected to compete with the messenger in terms of information carrying capacity it would have been even slower, and Donaldson would appear to have ignored the numerous instances of Roman forts sited very much further from outlying watch towers, with which they are obviously associated (e.g. Topping, 1987, 298-300 and Woolliscroft, 1988, 25-27).

The Gask tower spacings are, on the other hand, perfectly reasonable for a line of observation posts, for their overlapping fields of view would have permitted tight surveillance and between them, they allow almost every inch of the line to be watched. Despite the misleading term "signal tower", which is often applied to them, therefore, signalling would probably have formed only a minor part of their role. In this they would parallel certain modern deployments, for the writer is informed that observation posts on parts of the Green Line in Cyprus are set at very similar intervals and knows from experience that those on the former East German border were often even closer. Yet these are/were equipped with modern electronic communications for which no such range restrictions could be suggested.

In practice, like its present day equivalent, any small Roman frontier post faced with trouble would simply have wanted to contact the nearest garrison base (in this context the nearest fort) in the quickest way possible. For its role would have been to supervise and provide early warning, rather than direct defence. In studying any possible signalling system, therefore, we should probably bear this in mind and look for simplicity and efficiency, rather than complexity. We should also look to see how the forts themselves might have communicated with each other so as to allow the system to act as a single co-ordinated whole under emergency conditions and to facilitate a general troop concentration should a threat emerge at any one point that was beyond the capacity of the local garrison unit to handle alone.

We can now turn to the intervisibility details to see what pattern emerges. Doune cannot be seen from any other known Roman installation, although it does have a view into the heart of Stirling if, as still seems possible, a fort is to be expected there (4). This means that, for the moment, no signalling system can be traced beyond Glenbank (figs 1 & 2). This fortlet can be seen from Ardoch, however, and, although not visible from either Doune or Stirling, it stands in a reasonable position to link the fort to points further south. Likewise, all the known towers between Glenbank and Kaims also have direct views of Ardoch, as should the three additional towers that might be expected, on spacing grounds, between Glenbank and Ardoch, at around Balhaldie (NN 823064)(5), Kingfisher Hotel (NN 834080) and Kierallan Farm (NN 837089). In other words, the area is set up to allow the sort of direct signalling system already found on Hadrian's Wall (Woolliscroft, 1989a, 5-19) and the northern part of the Wetterau Limes (Woolliscroft and Hoffmann, 1991, 535-6) in which each minor installation has a direct link to a fort rather than signalling laterally from tower to tower along the line.

The position of Kaims Castle is slightly unexpected, although it may still have a certain logic. The fortlet stands at the northern end of a flat hill top which is the only point from which the forts of Ardoch and Strageath can both be seen simultaneously, so that a single installation here could have served as a relay point linking the two. But, standing where it does, Kaims is only just able to fulfil this role. The site has a clear view to Strageath (fig 3, A). But, even assuming that the fortlet was equipped with a c10m gate tower (Woolliscroft, 1993, 61-90), it would only have been visible from the very top of a similar tower at Ardoch, and even then only one at the southern end of the fort. The intervisibility is, thus, somewhat borderline and would have been easily blocked by tree or bush growth at the southern end of the hill top. Yet Strageath would have retained its easy view to Kaims even if the fortlet had been sited up to 350m further south, so it is somewhat surprising that Kaims was not built at the southern end of the summit, c320m to the south, from where the view to Ardoch would have been very much more secure. Nevertheless, the link between the two forts could still be operated by the fortlet as sited and Kaims may have been pushed to the absolute limit of Ardoch's field of vision in order to improve its own more immediate view north and/or to compensate, to some extent, for the fact that the hill is much closer to Ardoch than to Strageath. The ranges, with Kaims Castle as sited, are: Kaims-Ardoch 3.7km and Kaims-Strageath 6.6km, so that Kaims', at first sight illogical, position has shortened its distance from Strageath by c5%.

Westerton also has a direct view to Strageath and the two intermediate sites, which spacing considerations might suggest lie between the two, also seem likely to have done so, as would any intermediate tower between Westerton and Kaims. Again, therefore, this part of the system shows signs of having been efficiently laid out, with all of the known sites certainly enjoying direct views to a fort, and with the two forts themselves connected via a simple, one stage, relay. But we now come to look at the Gask Ridge itself.

Both Parkneuk and Raith can be seen from Strageath, but Raith, which stands on the western summit of the Ridge, is close to the eastern limit of view of the fort, even from a 10m tower. This means that for any signals from the rest of the Ridge top towers to reach Strageath, they would have to have been relayed via Raith. Interestingly, like Kaims, Raith could have been sited up to c350m further from the fort and still have remained visible but, again, there are good reasons for the site being built where it is. The tower, as sited (NN933185), has a quite spectacular field of vision, making it an excellent look out point as well as an important potential signal relay. Its view extends far to its west and north, allowing it to watch long stretches of the highland fringe. To its south and south-east it looks right across Strathearn to Kaims Castle, as well as controlling an excellent view of the floor of the Strath itself. But, perhaps most importantly, its view to the east takes in all the remaining ridge top towers as far as Midgate. Only to its north-east is its view somewhat limited. Yet, only 350m further to the east, the position would have been rather different, for after passing over this western summit, the Roman road starts to run a little way to the south of the Ridge top. As all of the towers are built close to this road, their views to the North become seriously degraded and a more easterly Raith would have been no exception.

In view of its excellence as a look out and signalling position, it is interesting that at least one Air photograph of Raith (Cambridge AKD-96) has shown what appears to be the ditch of a rather larger rectangular site (Plate 1, arrow 2) surrounding the modern water tank whose construction destroyed the known tower (arrow 1). This ditch is quite distinct from the well defined crop mark of a former plantation boundary (arrow 3), but has not yet been tested by excavation. It is, however, of just the right size and shape to be an additional fortlet of the Kaims Castle/Glenbank type and, although such an identification remains, at best, hypothetical, its possible implications will be considered in a moment.

The fact that most of the remaining ridge top towers lie behind the apparent optimum look out line, must, inevitably, reflect on the system's function. One might have expected a Roman frontier garrison here to have been primarily interested in what was happening to its north, and yet, of the eleven known towers on the Ridge itself, only Raith and Midgate have completely unimpeded views in this direction, even from tower top height.

The traditional explanation has been that the Ridge would have been heavily forested in Roman times and that the towers were designed to monitor, report on and, to some extent, control any movements across a cleared strip of ground around the road itself (Breeze, 1982, 62). In other words, they were designed to look east-west along the system, rather than to the north. It now appears that the level of forest cover in Roman Scotland may have been exaggerated in the past (Breeze, 1992, 331-5). But, whatever the local position may have been, it seems unlikely, in practice, whether there would have been that much need for such a watch, because anyone crossing the road from the north would already have had to reach and then climb the Gask Ridge itself and, although this is not especially difficult, the fact that almost no modern roads cross the Ridge is a reflection of the fact that there are very much easier ways through the area. The main route which, to judge from the temporary camps, all Roman invasions seem to have followed (Hanson, 1987, 121-7) passes through Strathearn, to the south of the Gask, along what is now the main A9(T) from Stirling to Perth. The only other viable route through the area is that followed by the modern A822 which passes quite close to Strageath and then runs due north through Crieff to enter the Highland passes at Fendoch. It is interesting to note, therefore, that all of the towers on the Ridge, no matter how poor their views north, have superb views over Strathearn and that, in many cases, these views would have been seriously worsened had the sites been positioned so as to obtain better views to the north. It may also be significant that Raith is positioned so as to enjoy particularly good views along the A822 and, although Christison's claim that the site can been seen from Fendoch (Christison, 1901, 28) is mistaken, it is visible from hills in the fort's vicinity. This raises a number of interesting possibilities and additional parallels with other frontiers.

Many of the towers on the contemporary Wetterau Limes also have limited views out from the line and, again, these sites almost all have superb views over their hinterland. This means that any invader entering the area, along the Fulda Gap, the most likely invasion route from the north, could be monitored and conspired against from the relative safety of the surrounding hills, so that the Limes could act, to some extent, as a defence in depth. This, in turn, would have made the defences more flexible and more able to maintain co-ordinated action after being penetrated than a shallow defensive line (Woolliscroft, 1988, 23-5), and the provision of special towers, apparently to facilitate cross Wetterau signalling, may be signs that these opportunities were exploited (O.R.L. Abt A, Band II,1, 1936, Strecke 4 & 5, 67-72. Helmke, 1910 and Kofler, 1898, 767-71).

It is possible that the Gask Ridge may have been intended to work on a similar basis, with the tower crews actually watching route ways and likely trouble spots from a safe distance, as well as simply monitoring their own immediate environs. If so, the superb, overlapping views to the north of Raith and Midgate, and the thorough observation cover of Strathearn provided by the rest of the Ridge top sites, would have put it in an excellent position to do so.

Such a possibility might also shed light on the system's relationship with the glen-blocking forts. For, if we are to see these installations in their traditional defensive light (Ogilvie and Richmond, 1967, 76), rather than as "springboards" (Breeze, 1982, 55-6) for assaults into the Highlands, that never materialised, their positions are such that most would have received almost no prior warning of attack.

Under normal conditions, one assumes that the Romans would have maintained intelligence cover ahead of their lines to give advance warning of any major attack (Woolliscroft, 1988, 23-7). But, in the fluid conditions that are likely to have existed for much of the Flavian period in Scotland, intelligence breakdowns could easily have placed the glen-blockers in serious jeopardy. For example, even if one accepts the supposed Fendoch tower as Roman(6), it could give the fort no more than a few minutes warning of a surprise attack down the Sma Glen, and the positions of other glen-blockers, where no such towers are even hinted at, would have been very much worse. For some, such as Bochastle, can see only a few hundred meters into their glens and so, even at full cohort strength, their garrisons could easily have become hostages to fortune. Midgate and Raith, on the other hand, could, between them, have watched over many miles of the same highland fringe, but from a range of about 10km, as well as guarding against flanking movements through Strathearn.

There is obviously little point in an early warning system if the warnings it provides come too late for effective counter measures to be taken. But the Gask Ridge is both far enough back from the highlands to give up to an hour's warning of any attack (even by horsemen) and close enough still to be able to see what was happening, at least during day light and in reasonable weather. In this context, although it is still possible to envisage a scenario in which the glen-blockers formed a distinct non-contemporary line replaced or proceeded by the Gask, it is also possible that the two lines could have usefully existed together, with the Gask representing a "back stop" frontier to which the glen-blockers were, to some extent, outposts.

To return to the signalling details; all of the Ridge top towers, as far east as Midgate (fig 2 and 3,B), can be relayed to Strageath via Raith (7), with Midgate itself occupying a knoll towards the eastern end of the Ridge with extensive views in all directions except, again, the north-east, the direction of Bertha. The site of Westmuir, the next tower to the east, on the other hand, is much more difficult to account for. The tower lies c920m from Midgate and is situated beside the Roman road, which again, here, lies a little to the south of the Ridge top. A section drawn from the 1:10,000 Ordnance Survey map would suggest that this position would also have been just about visible from Raith, but the writer's own survey contradicts this, and the tower is also out of sight of Bertha, to which it is closer than to Strageath (the half way point is close to Moss Side). Such a position does, of course, follow the pattern set by most of the other towers on the Ridge and, as ever, it has a good view to the south. But, from a signalling view point, one might have expected this site to be different, for only c300m to its north is the highest point on the whole Gask Ridge (NO 029210), the 154m eastern summit (fig 4).

Had Westmuir been built on this summit, it would have had considerable advantages. For example, without loosing much of its view to the south, it would have been visible from both Raith and Bertha, almost from ground level (fig 3,B), allowing a fairly simple two stage relay to link Bertha with both Strageath and Kaims Castle. It would also have had an even better view north than Midgate, which would have allowed it to see much further to the north-east along the Highland line, and east towards Perth and the end of Strathearn. Yet the opportunity was ignored, producing a tower with no view north, since it was over topped by the summit, and with limited views in every other direction except south.

Fortunately, on spacing grounds, the next tower to the east should lie somewhere in Cultmalundie Wood (cNO 040213). It cannot be stressed too highly that, at the moment, the very existence of such a tower is no more than hypothesis. The writer can find no trace on the ground and the dense woodland will make Air photography useless. But the gap between Westmuir and Peel does seem far too long not to have held intermediate sites and a considerable area of the wood can be seen from both Bertha and Midgate, as well as from Westmuir itself. Such a site would still not have been visible from Raith, however, and so any inter-fort communications between Bertha and Strageath would have needed to pass through a rather more inefficient three stage relay via Cultmalundie, Midgate and Raith.

To the east of Cultmalundie Wood the ground falls away rapidly towards Bertha and the Tay but, although contour maps would suggest that Peel and the 2-3 towers that might be expected between it and Cultmalundie, may just have been visible from Bertha, this could not be confirmed on the ground and so for safety's sake these links have not been included on the signalling plan (fig 2). These sites could, however, have been relayed to Bertha via Huntingtower, which does have a clear view of the fort and, as Huntingtower could also have relayed signals to Bertha from any sites between itself and Peel, the system, as a whole, is (depending on the existence of Cultmalundie Wood) potentially complete.

Midgate
(also called Thorny Hill)

Unfortunately, however plausible the above outline system may be, there is one problem which makes it impossible to accept without reservation. If we return to the dawn of archaeology on the Ridge, Christison's original programme included excavations at Midgate (NO 02112047), which was then the most easterly Gask site known (Christison, 1901, 32-5). Here, in addition to one of the standard timber towers, he also revealed a rectangular structure, which he took to be a second fortlet of the Kaims Castle type, lying immediately north of the Roman road and only a few metres east of the tower (fig 5). Yet, although Christison's report has remained the foundation for all subsequent studies of the area, this site seems largely to have been forgotten and, when mentioned at all, it is usually dismissed as non Roman, or even as a virtual figment of its excavator's imagination. Indeed, an observer of the calibre of O.G.S.Crawford (1949, 54-5) was able to visit the site and deny that anything was visible. But as the existence of a fortlet, at this particular site, could cast doubt on our model of the entire system, it was felt important that Christison's identification should be re-examined.

The Site

The importance of the site lies in its very close proximity to the Midgate tower, for its western ditch comes to within 13m of the tower ditch (fig 5) and it seems most unlikely that two Roman installations so close together could be exactly contemporary(8). Moreover, where a group of small Roman military sites, such as the Gask Ridge fortlets, form a distinct morphological class they might reasonably be expected to be contemporary inter-se, so that a date for any one installation is highly suggestive as a date for them all (9). This means that if Midgate is a fortlet of the same type as Kaims Castle and Glenbank, its position would cast doubts (in the absence of evidence to the contrary) as to whether any of the fortlets are likely to have belonged to the tower system.

The site lies at the eastern end of a small but distinct knoll, with its western half in the uncultivated south-east corner of a field and its eastern half in dense coniferous woodland. Despite Crawford's denial, it is still clearly visible as an earthwork (plate 2), although it has been heavily damaged since Christison's day by the imposition of a WWII building (11.13m x 5.8m) in its interior. It consists of a rectangular enclosure, almost identical to Kaims Castle, measuring 20m N-S x 23m E-W internally (Kaims measures 20m x 22m), which is rather more square than is shown by Christison's original plan (Christison, 1901, Fig 8). Like Kaims it is surrounded by the remains of an earth rampart which, as a surface feature, measures c4-5m thick, except in the west where it has been thickened to 11m since Christison's plan was drawn, perhaps in connection with the WWII activity. On lower ground, 7m (on average) out from the ramparts (again as at Kaims), a single ditch can be traced as a shallow hollow, c3.5m wide, around all but the south side, where it has been destroyed by the modern road. The orbit of this ditch is rather less regular than is normal for a Roman installation, but this is inevitable, especially in the north, thanks to the shape and steep sides of the hill.

As Christison (1901, 34-5) pointed out, the ditch is surrounded on its northern and eastern sides by a low mound. He interpreted this as a branch of the Roman road, to give access to the site, and his plan shows it continuing south past the site's SE corner to the modern road, which largely follows its Roman predecessor, but is here probably on a slightly more northern line. In fact, however, the feature begins to turn, parallel with the ditch, at this corner before being cut off with it on the south side of the site (fig 5) and, as it consists mainly of rubble from the partly rock cut ditches, it is clearly an upcast mound. There is also a causeway across the western ditch, a little north of centre, and immediately north of a narrow channel through the rampart, which gives the impression of being an entrance. Neither feature appears on Christison's plan, however, despite being conspicuously visible and so both seem likely to be modern. The channel, in particular, is probably meant for drainage of the interior and may again be connected with the WWII activity, and the causeway is probably its upcast mound. No other signs of an entrance survive, but this need not surprise us since Kaims Castle's entrance had been carefully blocked and was also invisible before excavation (Christison, 1901, 20). If the site is Roman, one would expect its entrance to have been on the south side, like that of the tower, facing the Roman road.

The Excavations

Christison's excavations were largely confined to the interior and produced similar results to Kaims Castle, with no buildings being uncovered, only the remains of paving. Unfortunately, this area has now been so badly damaged by a combination of Christison, WWII activity and exceptionally heavy infestation by Rabbits, that it was thought unlikely that further excavation would produce useful results. Work was, therefore, confined to re-surveying the site and sectioning the ditch, an operation that Christison does not appear to have carried out. Two trenches were dug (fig 5) which, for reasons of accessibility, were grouped around the ditch's north-west corner. T'1 (5m x 1m) sectioned the western ditch towards its northern end where it was just beginning to turn into the corner, whilst T'2 (4m x 1m) cut the western end of the north ditch, again just as it was turning into the corner. The two trenches were thus set at an angle of c70o and lay 7.6m apart at their closest.

Both trenches (fig 6) sectioned a "V" shaped ditch with a bottom slot or "ankle breaker". In both cases the ditch was 2.5m wide and a little over 1.2m deep (1.27m in T'1 and 1.21m in T'2). In T'1 the ditch had been dug into firm, but easily worked yellow sand, but in T'2 it was cut through a hard, if brittle, purple/grey sandstone, so that its bottom slot is unlikely to have been the accidental result of cleaning. In both trenches the ditch had been deliberately back filled with a slightly brown, grey loamy material (L2), probably degraded turf. This was identical to material currently being produced (in disturbing quantity) from the remains of the ramparts by rabbit activity, and was probably the result of the partial slighting of those ramparts. In both sections this layer was essentially homogenous, but both showed a fair degree of gradation, with a preponderance of finer particles towards the bottom, consistent with a long period of water action since backfilling. In T'1 the backfill filled the entire ditch, with no detectable sign of primary silt, even in the bottom slot. This, coupled with the very sharply defined sides of the sand cut ditch, suggest that the ditch was back filled almost immediately after being dug, or re-cut. T'2 showed a deep silt deposit, some 0.5m thick in two layers. The lower, and much the thicker, was a 0.4m deep layer (L5) of silty purple/grey sand, similar to the weathering product of the natural bed rock, which in the area immediately outside the ditch had weathered to produce a thick (c0.2 - 0.25m) layer of soft, but here clean, purple/grey sand. Above this, the northern 2/3 of the ditch were covered by a c0.1m thick layer (L4) of clean grey silt. The boarder between these layers was somewhat vague, but that between them and the the backfill (L2) was very clear cut, so that the two trenches taken together may suggest that the ditch was open and subject to natural silting for some time and then backfilled whilst in the process of being cleaned out. No dating evidence was found, but this activity must have taken place long enough ago for the backfill to have been graded by water action.

Interpretation

In the absence of datable material, one cannot honestly claim that the excavations prove a great deal. Perhaps the most that can be said is that nothing was found in either trench or in the general layout of the site that is other than consistent with a Roman fortlet. Unfortunately, however, a "V" shaped ditch, even one with an ankle breaker, is not necessarily diagnostic as Roman in northern Britain because a number of sites of Iron Age date, or at least culture, have also produced such ditches (for example Cnoc a' Caisteil near Alness, (Rideout, 1987, 68) and Hartburn, Northumberland, which was itself once thought to be a Roman fortlet (Jobey. 1973, 17.)). Taken together with the surface survey and Christison's results, however, the very close similarity of Midgate to Glenbank and Kaims Castle appears to make it virtually certain that these near identical, sites form a distinct class, which although presumably contemporary inter-se, do not fit comfortably with the towers. Indeed the writer would wonder whether there would ever have been any doubt over this if Midgate had not been so close to its tower. Furthermore, the Air evidence from Raith (plate 1) may, as stated, present a fourth member of this class, occupying the same site as a known tower and, therefore, actually over (or under) lying it. It is important to remember that none of these sites has yet produced dating evidence and despite its traditional identification as such, Kaims Castle is no more certainly a Roman fortlet than Midgate. A firm absolute and relative dating (vis à vis the towers) must, thus, await further excavations, especially at Raith and, in the mean time, we can only use what evidence we have to weigh up the possibilities.

The site of Midgate itself is not as helpful as might have been hoped, because the tower and fortlet are just far enough apart to remain completely separate. Their ditches do not intersect and, so far as can be seen, neither of their ditch upcast mounds overlies the other. It is, therefore, impossible to establish a relative dating between the two sites and we are left with a process of elimination between pre-historic, Roman and post-Roman dates for the "fortlets".

A non Roman date has been advocated to the writer in a number of private conversations but, although the possibility must continue to be borne in mind, it does seem somewhat improbable. This is partly a subjective conclusion, because the "fortlets'" general form coupled to their, albeit non conclusive, ditch profiles appears so Roman, but it is also based on their relationship with the Roman road. For, whilst these are the only such sites known in the area, all are within a few metres of the road. Two have their entrances oriented towards it (Christison, 1901, (fig 2) and Maxwell 1990, 353-9), and, whilst the position at Raith is uncertain, even Midgate, whose entrance is unknown, lies parallel to it. It would, thus, appear most unlikely that these sites could have been constructed before the road was built, or at least planned, which tends to rule out a pre-historic date.

A post Roman date might be more conceivable, although again the sites' morphologies argue against it. But, although such a date cannot be ruled out, severe doubt is cast over it by the apparent presence of a unit of six Roman miles (8877m) in the sites' spacings. Glenbank and Kaims Castle are almost exactly six Roman miles apart, and Midgate is 12 Roman miles from Kaims, six Roman miles from Raith and six from the fort at Bertha(10). The use of this unit by non Roman builders seems unlikely, whilst the very presence of such a systematic approach would make a Roman date more probable, especially since the degree of gradation in the Midgate ditch fill rules out relatively modern dates.

If we, therefore, assume that the "fortlets" are Roman, the choice is between the Flavian and Antonine periods, the times at which the system's forts were occupied. For the moment, it must be stressed that the evidence for either (or indeed any) period is inconclusive, but although the traditional Flavian date may still be considered more likely, it is worth reviewing the evidence, if only to remind ourselves that the case is unproven and to suggest areas in which further data could be sought.

A Flavian date would certainly be more convenient because, although it would complicate our present picture of the system, it would leave its fundamentals unchanged. We would simply have to envisage a process of development in which fortlets were added to a system of towers and forts, or in which towers were added to one of forts and fortlets. The former, in particular, would leave the signalling arrangements discussed above substantially unchanged and there is a certain amount of evidence that might support such a scenario. For example, we have already seen the recurrence of a unit of six Roman miles in the system, and it is noteworthy that Glenbank is six Roman miles from Doune, the only fort on the system that has, so far, shown no sign of re-occupation in the Antonine period (Maxwell, 1984b, 217-24). More persuasive evidence might be seen in the fact that there is no sign, as yet, that either Kaims or Glenbank replaced towers, and that Glenbank, like the towers in its vicinity, has a double ditch. It is always dangerous to argue from an absence of evidence and the Glenbank ditch could, of course, be coincidence, but this does seem to link the southern fortlets more closely to the towers and may suggest that a change was made to the system's overall plan during the course of its construction. If so, it would appear that the Gask Ridge sector itself was built first, for whilst at Midgate and Raith fortlets may have replaced towers (or possibly vice versa) that had already had time to be completed, Kaims and Glenbank seem to have been built together with their surrounding towers, which may all, therefore, be slightly later. Furthermore, G. S. Maxwell (1986, 354) has recently sought to establish a rational spacing system for the towers in the southern area, based on the north gate of Ardoch, and of which Glenbank and Kaims seem to form an integral part. All this should have helped to tie the system together once and for all but, unfortunately, it is still unproven whether these double ditched southern towers are themselves Flavian. Only the single ditched towers have so far produced dating material and, as these show no such regularity in their spacing (Table One), the two types need not necessarily go together.

An Antonine date for the "fortlets" would force rather more of a change in our model. Current thinking envisages a Flavian system of forts, fortlets and towers and an Antonine system of forts only, with no signalling links between them, because none of the forts are intervisible. Antonine fortlets, would change this to an arguably more balanced picture with a Flavian system of forts and towers and an Antonine system of forts and fortlets. Such a use of small fortlets as road posts is hardly unknown in Antonine Scotland and three, admittedly tenuous, strands of evidence could be marshalled in favour of an Antonine date.

Firstly, there is a general tendency for small fortlets of this type to be more of a second than a first century phenomenon. For example, Maxwell (1990, 353-9) compares the standard picture of an integrated Flavian Gask Ridge system with fortlets, to the Flavian system on the Wetterau Limes in Germany. Yet it is noteworthy that, where they have been investigated, the Kleinkastelle of the German Limes have often proved to be later than the original Flavian design (Baatz and Herrmann, 1989, 374-423) and usually date to the 2nd century. Similar tiny fortlets proliferated in the mid second century, as milecastles or Kleinkastelle on the frontiers, as road posts in their hinterlands, or as components of coastal defences (Bellhouse, 1989 and Newall, 1976, 111-23). First and early second century fortlets, on the other hand, are rarer and usually larger, as can be seen at Haltwhistle Burn (Gibson and Simpson, 1909, 213-85), Cargill (Richmond, 1943, 47-8) and Castleshaw (Walker, 1989). Milecastle sized fortlets do occur in the first century, for example at Old Burrow and Martinhoe in Devon, (Fox, 1977, 15-20) but they are much less common.

A second strand of evidence stems from possible parallels between the interiors of Kaims Castle and Midgate, and some of the milecastles of the Antonine Wall. Christison (1901, 21 and 33-4) expressed surprise that he could find no sign of internal buildings in these "fortlets", and this continues to cause puzzlement. Christison had pioneered the excavation of timber features in Scotland (Christison and Cunningham, 1898, 443-6) and was, thus, quite capable of finding such buildings. Yet in both "fortlets" he found only a paved interior. It does not, however, seem to have occurred to him to look under this paving for signs of an earlier period which may have involved buildings. This is a pity, because in recent years a number of Antonine Wall milecastles have been found which had had their interiors cleared of buildings and paved over at some time after their completion. The milecastles picked out for such treatment (Wilderness Plantation, Kinneil and possibly Seabegs Wood (Wilkes, 1974, 57. Keppie and Walker, 1981, 145-6)) are all in important potential signalling positions (Woolliscroft, 1993, 208-307) and the Gask Ridge "fortlets" may have had a similar history. Kaims Castle, in particular, could have been vital for signalling and it would be interesting to see what a re-excavation of the site might reveal.

The third piece of evidence is the most tenuous of all. It has long been fashionable to use spacing criteria and the relationships between known Roman installations to help in searching for new ones. The value of such numbers games may sometimes be debatable, but we have already seen the recurrence of a unit of six Roman miles in the spacing of the Gask Ridge "fortlets" and in their relationship to the forts of Bertha and Doune. It was already because of this pattern that the writer sought out the Air photograph of Raith (Plate 1) discussed above, and if projected further south it would also place installations on the long suspected sites of Stirling and Torwood (cNS 834846). The principle interest, however, would lie in the fact that a further six mile spacing to the south of Torwood would project as the base of the system, not the Flavian founded fort of Camelon, as might be expected, but the Antonine Wall fort of Mumrills.

The evidence from signalling is ambiguous, even if we are right in thinking that there actually was such a system in place. Certainly, it might be thought odd if the Antonine forts were left without relay sites to provide inter-fort communications, and if the Antonine system had used isolated relay stations, rather than a closely spaced line of watch posts, fortlets would have been a safer (in modern parlance "harder") size of installation to use. But there is a problem because, although the "fortlets" come tantalisingly close to being able to provide such links, they do not quite manage it and this must throw doubts on their relevance to an Antonine context.

The problem, once again, is the failure to occupy the eastern summit of the Gask Ridge, to the north of Westmuir. This appeared peculiar enough on a Flavian only system, where it merely produced an unnecessary degree of inefficiency, but on an Antonine fort and fortlet system it would have been fatal. For, although Kaims can link Ardoch to Strageath, Raith (if it exists) can link Strageath to Midgate and Glenbank can link Ardoch to points further south, Midgate's view to Bertha is blocked by the Ridge summit so that one of the system's forts would have been left cut off. The puzzle would, thus, be: if the "fortlets" are Antonine, why was Midgate not built on the higher ground to its north-east so as to link Raith and Bertha and allow the whole system to work ?

There are two possible solutions, but neither appears very satisfactory. For example, it could be that there actually was some sort of minor installation outstationed on the summit that we have simply not yet found. But this seems unlikely if only because it would have been such a needlessly complex arrangement. The summit is only 7m higher than the "fortlet". Midgate is already fully exposed to the prevailing westerly wind, so it would have gained little in the way of shelter by being positioned off the highest point and, as both Raith and Kaims are sited on hill tops, there seems to be little reason why Midgate should not also have been.

The second possibility rests on the weakness of the evidence for an Antonine occupation of Bertha (Adamson and Gallagher, 1986, 195-204). Excavations at the site have, so far, produced only a single phase of defences and all of the stratified pottery is Flavian. The only evidence for Antonine activity is a single sherd of probable Antonine pottery, picked up as a surface find, and a dedication to Disciplinae Augusti found in the river (Keppie, 1983, 402) which, although undated, is of a type which does not occur before Hadrian and is generally Severan (R.I.B. 990, 1128, 1723, 1978, 2092).

Obviously, if the fort did not, in fact, have an Antonine phase, there would be no need for any signalling arrangements to include it. But even this is not quite enough, because if this were the case Midgate would become the terminal installation of the system. This might be surprising in its own right (although not impossible) as the site would be only a fortlet. But one would certainly expect that, if the terminal site of such a line was given the opportunity of being sited on a magnificent position with a superb view towards exactly the direction from which any major trouble might be expected to come, it would take it. If this site could also have provided observation cover, from a safe distance, of Bertha and a greater area around it than the fort itself could command, one would have expected it to be doubly tempting. In other words, even if Bertha had not existed, one would expect that, if Midgate was part of a system consisting only of forts and fortlets, it would still have been built on the Ridge summit, even if now for totally different reasons(11).

There is also another difficulty. Antonine fortlets at Midgate and Raith would leave our model of the Flavian system unaffected, thanks to the presence of towers. But, if Kaims Castle was Antonine there could be no general signalling system on the Flavian line since this site, which is the only possible link between the forts of Ardoch and Strageath, has no corresponding tower. This, however, is to begin to enter a circular argument since, despite mapping a possible Flavian signalling system we still cannot be sure that one ever existed, or was even aspired to. Under these circumstances, all that can be said is that, whilst the Gask Ridge's minor installations do seem to make most sense in the, traditionally envisaged, single period, probably Flavian, context, there are peculiarities even here and the exact position will only be known when a good deal more excavation and Air reconnaissance work has been carried out.


Acknowledgements

The writer wishes thanks Messrs Ian Brown & Sons, the owners of Midgate, for permission to carry out excavations and Dr S.A.M. Swain for her help in the field.

Notes

1. Greenloaning, Westmuir, Peel and Huntingtower are only known from Air photography, although there seems little doubt as to their identity. [Return to text]

2. G.S.Maxwell (1990, 354) mentions amphora fragments from Glenbank but has yet to publish their date and context. [Return to text]

3. The results of the excavation were surprising because the site stands on an exposed hill top with a superb view over Stirling to the Highland fringe, a marvellous signalling position but an unpleasant place to live. [Return to text]

4. It is still not certain that Doune is part of the Gask System. Its discoverer (Maxwell, 1990, 353-9) has suggested that it might do away with the need for a fort at Stirling, but the two are six Roman miles apart, the same as Ardoch and Strageath. They would also have had complimentary roles because Stirling, the traditional gateway to the highlands watches the primary route over the Forth, whilst Doune guards an ancient secondary pathway through the extensive Forth mosses. [Return to text]

5. The R.C.A.H.M.S. Sites and Monuments Record 6" map records a ring ditch at this reference discovered from the air in 1984 which may be the missing tower, but the writer has been unable to obtain further information. [Return to text]

6. The site is unexcavated, but its prominent central mount and faint outer ditch do not look like any other Flavian tower. It stands in a cairn field and until the 1770's had five standing stones on it. In 1783 large amounts of stone were removed to build a bridge over the Almond (O.G.S.Crawford, 1949, 48-9). Yet all other Flavian towers in Scotland are built solely of timber. As for its position, the site can see Fendoch but not the newly discovered putative fortlet (information from G.D.B.Jones) which stands only a few hundred metres away. Its famous view up the Sma Glen is actually extremely limited even from the height of a Roman tower, perhaps no more than c400m. The site is also some distance from the fort and a vastly superior site can be found on the opposite (northern) side of the Glen mouth from where a tower would have had a dramatically improved view up the Glen and a view to the fortlet, whilst being much closer to the fort. [Return to text]

7. It has been the writer's usual policy not to cite any intervisibility that has not been personally checked in the field but, as much of the Ridge top is heavily wooded, the intervisibilities between Raith and the sites to the east of Kirkhill have been checked using 1:10,000 contour maps. The maps would suggest, however, that the views would have been very clear with no borderline cases. [Return to text]

8. Christison (1901, 32) attempts to get around the issue by describing the tower as an outwork of the fortlet. [Return to text]

9. The entire tower system has, after all, been dated on precisely this basis. [Return to text]

10. The spacings are exact to within 1-3%. Within this margin the sites appear to have been sited in accordance with local tactical considerations. It is noteworthy that the forts of Camelon, Ardoch and Strageath do not fit into this sequence. Ardoch and Strageath are also six Roman miles apart, but Kaims lies much closer to Ardoch than to Strageath and Glenbank is much closer to Ardoch than Doune. The measurements are scaled from maps and thus subject to inaccuracy due to the unevenness of the ground, but as the difference between 6 Roman and 6 statute miles is c725m, almost half a Roman mile, it is unlikely that the two units could be mistaken for one another. [Return to text]

11. It might also be interesting to speculate as to why the WWII installation was not built on the Ridge summit, since the writer is informed that it was an anti-aircraft position. [Return to text]

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Figures

1. The Gask Ridge System

2. The Signalling System of the Gask Ridge, Schematic Drawing

3. Sections Through the Terrain of the Gask Ridge System to show Site Intervisibilities

4. The Topography of the Eastern end of the Gask Ridge

5. The site of Midgate as a surface feature, showing the tower and fortlet and the positions of the two excavation trenches T' 1 and 2

6. Midgate fortlet, the excavated ditch sections. It should be noted that points B and X and both on the inner side of the ditch (see fig 5) 1 = Turf and Topsoil, 2 = Grey gritty loam, 3 = Yellow sand, 4 = grey silt, 5 = Plum/grey sand, 6 = Grey sandy loam.

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