EXCAVATIONS AND SURVEY AT THE RING DITCH OF EAST COLDOCH, BLAIRDRUMMOND
D.J.Woolliscroft and N.J.Lockett
East Coldoch was discovered from the air by the RCAHMS as a ring ditch of approximately 30m in external diameter and damaged by the insertion of a modern water tank. It is located in plough land and nothing is now visible on the surface, but air photographs show an ovoid form, somewhat narrower east-west than north-south and with a single entrance break oriented towards the Northeast. The site lies at NS 703986 (fig 1a) on the summit of a low hill which, although only 41m high, offers a superb vantage point, with long range views in all directions, especially to the south, over the Forth valley and the hills beyond with, for example, Stirling Castle in full view at a distance of 10km to the ESE.
The writer originally became interested in the site during a search for possible Roman towers south of the known Gask series, and especially between Stirling and the fort of Doune, where they might also help to trace the routes of any Roman roads. The available air photographs showed the site to be sitting amongst a number of lighter ditched structures, usually classified as Iron Age homesteads and palisaded enclosures. Fig 1b shows a number of these, with one small ring ditch immediately to the right of the site and a faint, but much larger, ditch apparently intersecting the site’s own ditch. Another large (apparently multi phased) ditched enclosure is visible to the right of the picture, on the other side of the modern road, as are a number of what appear to be posthole structures. The site itself is interpreted as a ploughed out barrow or ring ditch house on the NMRS record sheet (NS79NW 34), but its ditch stood out in marked contrast with its neighbours, being markedly heavier, which, coupled to its vantage point, raised the possibility of a Roman military installation superimposed amongst a group of native features.
With the kind permission of the farmer, Mr J.Graham, a resistivity survey was conducted in 1996, which confirmed the ovoid form and the estimated dimensions, derived from the air photographs (fig 2). The site is 29m in external diameter east-west and approximately 32m north-south, although interference from the modern water tank and disturbance, which may have been caused by the still more recent burial of its concrete cap, made the results in the southernmost part of the ditch circuit less than clear. The entrance break is roughly 10m wide and shows a slightly tucked in appearance caused by the southern ditch butt end being positioned noticeably to the west of its northern counterpart. The ditch appeared to be about 4m in width, which would leave an internal area of around 21m x 24m. Air photographs had shown a dark area in the centre of the interior, which might represent a filled in hollow of some sort, and the resistivity plot shows a corresponding area of low readings. It also, however, shows a band of readings, just inside the ditch, which are higher than the normal background for the field and which might represent the remains of an internal rampart. Finally both the survey and the air photographs show a number of modern pipes, including two running c. 5.5m apart, which cross the site on a near parallel path from the Southwest to the Northeast and pass through the ditch entrance break. These approach the modern water tank and had been interpreted as water pipes from the air photographs, but the resistivity survey was able to trace them running straight past it, and they now seem more likely to be field drains.
Once the resistivity survey had been plotted, a single test trench was excavated to section the ditch at the northernmost end of the site (fig 3). This revealed a substantial, flat bottomed, “U” shaped ditch, 4.3m wide and 1.6m deep. Immediately inside and parallel, to both this feature and to each other, two slots were located, each of which produced a single post hole within the 1m width of the excavation trench. The outer (northernmost) of the two was the broader by a small margin at 0.25m (as against 0.21m) and the features lay 1.04m apart at their centre lines. The two slots appeared contemporary both with each other and with the ditch, since both were cut into the same natural layer (fig 3, L 14) and both were overlain by the same loam and charcoal deposit (L’3), whilst the outer slot had been cut into the inner ditch lip, apparently whilst the latter was open. If this interpretation is correct, they may represent either a double internal fence of some sort (such widely spaced uprights can hardly be called a palisade), or possibly some form of box rampart. It remained possible, however, that they were simply successive fences.
The only post hole within the slots whose original form could be ascertained was that shown in plan in the inner feature (fig 3). The timber here had been stone chocked and had rotted in situ. It was rectangular in section, measuring 0.15m x 0.12m. It was sunk just 0.36m into the subsoil (it appears shallower in the drawn section which was measured against the trench side) and set at an angle of almost 45o to the lines of both the ditch and its own slot. None of this would suggest a timber designed to support a box rampart of any weight, but then the two slots are too close together to provide for more than a fairly lightweight fill content. Even so, if we are dealing with a box rampart, its southern side, at least, must have been fairly low to have been adequately supported by such a post. On the other hand, the single posthole found in the outer slot was rather more substantial. Here the post itself was missing, so no exact dimensions can be given, but the post hole was considerably deeper, at 0.67m, and at least slightly wider at 0.16m which suggests a rather stronger arrangement which should have been able to support a greater depth of rampart.
The only real evidence for a rampart, however, apart from the resistivity data, lies within the ditch fills. The ditch had initially begun to silt naturally, probably over a considerable period, with a thick (up to 0.35m) layer of grey, waterlogged, primary silt (L’13) overlain by an equally thick, fairly even, layer (L’11) of gravely grey loam. These deposits, however, had then been partly buried by two layers which had clearly slumped into the ditch from the site’s interior. Layer 9 was a band of mixed turf, which still preserved a complex jumble of carbonisation lines whilst, below this, layer 10 was a loose deposit of clean brown loam which appeared to have collapsed or been dumped into the ditch in one event rather than being washed in over time. Layer 3, a plough truncated deposit of grey/brown loam with charcoal flecks, which sealed the two post slots, might also have been turf derived and all of this would sit well with a rapid demolition or collapse event, perhaps involving a turf and earth bank or the contents of a turf filled box rampart, for which the posts might have formed a revetment. Moreover, the surviving shape of the top of the outer slot’s post hole might suggest that the post had eventually snapped off at, or just below, ground level and then fallen, or been pushed out into the ditch, whilst the relatively small volume of material involved in these layers would again suggest that only a relatively slight rampart was involved. It seems possible, therefore, that we might be dealing with the remains of a turf bank of some sort, which may have sloped down from the ditch face into the interior, hence the lighter timber revetment at its lower inner face. It might be equally likely, however, that the heavier posts on the outer face were provided simply because the rampart approached so close to the ditch lip and required greater stabilisation here to prevent its being undermined, rather than because the physical weight of material was greater. Whatever the case, it is not hard to see why the site’s builders should have wanted to both constrain the width of their rampart and to place it so close to the ditch. For, even as things are, the feature would have reduced the size of the internal area to around 19m x 22m and a more conventional turf rampart would have reduced it still further.
Finally, there was no obvious sign of a buried topsoil, vegetation layer or similar deposit at any point to suggest that the ditch had stood open for any significant period after the rampart collapsed. Layers 6 and 12 against the outer face of the ditch were small lenses of gravely material which appeared to have been dumped, but the rest of the ditch fill, (L’s 2, 5 and 8) is made up of loam deposits which may have entered the ditch through plough action It is possible that material may have been dumped into any surviving hollow when the water tank was cut into the site, but the present farmer has only been on the land for a few years, which means that there is no family tradition to record what the site might have looked like before the tank was installed. The writer has, however, been unable to find any reference to the ditch being visible at the surface within near modern times, let alone within living memory.
No datable material was found during the excavation and although flecks of charcoal were recovered from layer 3, there was no material suitable for carbon dating within any context that could be confidently regarded as primary. It is, thus impossible to make more than an intelligent guess at the site’s date and identity. Certainly, the ditch is somewhat large for a Roman tower, but not abnormally so, for the tower of Garnhall on the Antonine Wall has a not dissimilar external diameter at 28.97m (Woolliscroft in Keppie 1996, 400f). The ovoid shape is also not unprecedented for a Roman site in this area since the Gask tower of Midgate (Christison 1901, 34f and Woolliscroft 1993, 302ff) has a similar form, albeit the identity of this site has been challenged in recent years (Hanson and Friell 1995, 514). The size and form of the entrance break would, however, be highly unusual for a Roman tower, where symmetry and an entrance width of only 3-5m is the norm and the ditch would appear to be both too substantial and of completely the wrong shape to represent a minor Roman military site. If anything it resembles a ditch found some years ago at the North Mains of Strathearn henge (Barclay 1983, 134, fig 10, section E-F).
The site does, however sit amongst a group of features which appear to be Iron Age in date and the Coldoch Broch lies only c.850m to the Southwest, which means that the traditionally envisaged Iron Age date remains eminently plausible. That said, however, the ditch does appear rather heavy for a homestead site and especially for one with such a small internal diameter, and so the possibility of a small Medieval defensive site, such as a motte, might also be worth considering. Hopefully further work will be possible in future to study the interior, which although damaged by the water tank should still be substantially intact, and so it would appear prudent to leave any further interpretation until then.
Barclay, G J 1983 “Sites of the third millennium bc to the first millennium ad at North Mains, Strathallan, Perthshire”, Proc Soc Antiq Scot, 113, 122-281
Christison, D J 1901 “Excavations Undertaken by the Society of Antiquaries of Scotland of Earthworks Adjoining the ‘Roman Road’ Between Ardoch and Dupplin Perthshire”, Proc Soc Antiq Scot, 35, 16-43
Hanson, W S and Friell, J G P 1995 “Westerton: a Roman Watchtower on the Gask Frontier”, Proc Soc Antiq Scot, 125, 499-520
Keppie, L J F 1996 “Roman Britain in 1995, Scotland”, Britannia, 27, 396-405
Woolliscroft, D J 1993 “Signalling and the Design of the Gask Ridge System”, Proc Soc Antiq Scot, 123, 291-314