Introduction
On 1 March 1975, at the 7th meeting of the Scottish Archaeological Forum, John Gillam delivered a game-changing paper entitled ‘Conception and afterthought on the Antonine Wall’.1 It was published the next year as ‘Possible changes in plan in the course of the construction of the Antonine Wall’.
‘Until within the last decade’, Gillam opened, ‘the Antonine Wall tended to be thought of as having been planned and executed according to a single concept’ (Gillam 1975: 51) – a concept, to be sure, that had always seemed very different from the one underlying the just abandoned frontier across the Tyne-Solway isthmus. For one thing, the Antonine Wall appeared to lack a regular cordon of small installations equivalent to Hadrian’s Wall’s turrets and milecastles. Instead, the new frontier in Scotland boasted a total of at least 17 forts, many of which were significantly under full-regiment size.
For a frontier only half the length of Hadrian’s Wall, this resulted in an average spacing of just over two Roman miles. The Antonine frontier in Scotland, in short, had always seemed a different animal.
In a radically new departure, Gillam argued that the original plan for Pius’ new frontier had provided for six normal-size forts only, identified as Carriden, Mumrills, Castlecary, Bar Hill or Auchendavy, Balmuildy and Old Kilpatrick, four of which could be shown, or argued, to be earlier than the adjoining sections of the Antonine Wall. With intervals between them in the range of c. 7-9 miles, the initial arrangement would in fact be remarkably similar to the preceding disposition on Hadrian’s Wall.
What the new frontier also replicated from its predecessor, Gillam suggested, was fortlets acting as fortified gateways. Sites like Watling Lodge, Wilderness Plantation and Duntocher were clearly part of the original plan and obviously akin to Hadrian’s Wall’s milecastles. At Duntocher, the fortlet was succeeded by a small fort, while the possibility of a similar juxtaposition, and implied succession, was noted at Rough Castle and Castlehill. On this basis and working with a limited set of distances, Gillam hypothesized a regular series of fortlets, at average intervals of 1.1 Roman miles. About half of these, his thesis implied, would in time have been replaced by the other known forts. Five of these ‘secondary’
installations, Gillam stated, could be shown to be structurally later than the Antonine Wall Rampart that formed their north face.
1 Sincere thanks are due to David Breeze, Michal Dyčka, Nick Hannon, Bill Hanson, Rebecca Jones, John Poulter, Sebastian Sommer, Matt Symonds and Andrew Tibbs for sharing thoughts and information. For the final version, I was able to see the submitted text of Nick Hannon’s PhD research (2018), for which I feel deeply indebted to him. Regrettably, Bill Hanson’s reply (forthcoming) to Graafstal et al. 2015 came too late for a response. In this paper, distances are normally given in metric style, while unspecified miles are always Roman (1.48 km). The shorthand terms ‘Ditch’, ‘Berm’ and ‘Rampart’ (with a capital) refer to these components of the Antonine Wall.
The Antonine Wall: Papers in honour of Professor Lawrence Keppie: 142–185
A singularly influential thesis was born – and what is more, a thesis that could be put to the test.
Gillam’s proposal catalysed the big fortlet ‘hunt’ of the late 70s: within five years, a handful new fortlets were discovered at Kinneil, Seabegs Wood, Croy Hill, Summerston and Cleddans (Hanson 1979;
Keppie and Walker 1981; Maxwell and Hanson, this volume). The new harvest also boosted confidence in the fortlets that were suspected to be hiding in the ‘arm-pits’ west and east of Castlehill and Rough Castle, respectively, which now appeared to be indicated by pertinent terrain features (Keppie 1980:
83-4 with fig. 1; Hanson and Maxwell 1986: 107-8).2 At Croy Hill, the local sequence seemed to provide robust support for Gillam’s model, with the fortlet firmly bonded with the Antonine Wall Rampart and the fort, some 80m to the east, clearly coming later, as demonstrated by its east rampart overriding a well-like structure with an overflow that passed through the base of the Antonine Wall Rampart (Macdonald 1932: 257-59).
With the support of all this new evidence, Gillam’s hypothesis conquered the field in the early 80s.
It was favourably discussed in several influential reviews (e.g. Keppie 1980; 1982) and embraced in the new standard work on the Antonine Wall by Hanson and Maxwell first published in 1983 (1986:
105-12). The version that has become established since, in both academia and public outreach, is of an Antonine Wall undergoing an incisive change of plan, while still under construction, by the addition of a dozen or so ‘secondary’ forts. It is interesting to see how the logic of the two successive plans has since tended to structure scholarly debate by making it focus on remaining problems, like whether Bar Hill or Auchendavy had the best credentials for being ‘primary’ (e.g. Keppie and Walker 1985: 32-3), or by prompting the suggestion that the two stages of the Antonine Wall might account for the fact that multiple units are attested at some of the ‘primary’ sites (Hodgson 1995: 34).
But the Antonine Wall landscape of evidence is varied and ambiguous. To stay with the sites where multiple units are attested, this group also includes Bar Hill which Hanson and Maxwell had good reasons to label as ‘secondary’ (1986: 106). Their discussion of the Gillam hypothesis was duly nuanced.
It contained the crucial observation that the primary/secondary divide does not coincide with the
‘complete regiment’ versus ‘vexillation’ size classes of forts, ‘secondary’ Cadder and Castlehill falling in the former category (Hanson and Maxwell 1986: 105). Hanson and Maxwell also noted that the change of plan apparently came very early in the sequence, seeing that the linear works in one of the early legionary lengths anticipated the causeway and bonded with the fort rampart of Rough Castle (1986:
107, 134-35). Finally, the important reservation was made that the different structural relationships between the forts and the linear works could be down, in large part, to varying progress between the different work squads (Hanson and Maxwell 1986: 109) – a point, it may be noted, that had earlier been used to underpin the ‘single concept’ version of the Antonine Wall (Robertson 1979: 30-1).
Looking back on four decades of dissemination of the Gillam hypothesis, it is striking to see how relatively subordinate the place of terrain and topography has been in most discussions, whether on a site or a systemic level. Only in the last decade has the landscape finally come to the fore. A signal contribution has been John Poulter’s analysis of the planning principles underlying the sinuous course of the Antonine Wall which, he argued, implied knowledge of all the major installations, including most ‘secondary’ forts (2009: 90-130). Poulter’s study also serves to underline the necessity of a systems-analysis approach to Roman artificial frontiers. Most limites were highly complex systems, the constituent building blocks of
2 But see Macdonald 1933: 260, for the enclosure at Rough Castle as ‘an integral part of the Antonine fort’ and, for Castlehill, Hanson and Jones, this volume.
which could be dependent on several other factors, like planning order, alignment, spacing, operational requisites and, not least, intervisibility – a property curiously ignored in most Antonine Wall studies (pace Woolliscroft 1996). The resulting web of structural, spatial and logical dependencies can become a strand of evidence and insight in its own right, much like a real archaeological stratigraphy. For the Antonine Wall, the potential of this ‘sequential stratigraphy’ is still largely unexplored.
The basis for this paper was laid during a study tour of the Antonine Wall, in October 2014, in the company of David Breeze, Rebecca Jones and Matt Symonds. With all this energy and knowledge on board, our excursion started with paying homage to the dedicatee of this volume at Old Kilpatrick, Carleith and Cleddans – and then still managed to cover most of the other fort and fortlet sites in just two days, typically continuing in the evenings with lively discussion of the thoughts and observations collected on the way. From the first, our focus was on the system’s topography and terrain settings.
With three of the participants heavily imbued with Hadrianic rigidity, perhaps what impressed us most was the Antonine Wall’s subtle dialogue with the landscape. Dialogues can be revealing of underlying concerns. To name just one example, in the more broken terrain west of Balmuildy, we were struck by the system’s dominant south-facing orientation, with the installations often set to control a maze of valleys that opened up to the Clyde basin.
The direct outcome of the 2014 excursion was a paper that questioned some of the traditional supports of the Gillam hypothesis, while highlighting the Antonine Wall’s topographical sensitivity and consistency of planning, ‘secondary’ forts included (Graafstal et al. 2015). The main arguments of the article, cheerfully titled ‘Sacred cows in the landscape’, were discussed at a themed session of the Roman Northern Frontiers Seminar at Edinburgh in May 2016. The present article is an expanded version of the paper read by the author on that occasion. Up to that point, the underlying terrain analysis had been based on low-resolution elevation data provided by ESRI. The situation was greatly improved when, in the summer of 2017, the Environment Agency released a series of LiDAR datasets for lowland Scotland at resolutions up to 0.5 m2 which covered most of the Antonine Wall. For their analysis, the author has used the tools for Digital Elevation Models provided in the QGIS package.
Structures or system?
One of the points of the ‘Sacred cows’ paper was that the structural relationships between the forts and the linear works are far from consistent (Graafstal et al. 2015: 56-9). A case in point are fort causeways. At Castlecary and Balmuildy, generally ranked among the first installations to be built on account of their stone ramparts, the causeways over the Ditch consisted of undug earth, confirming the early planning of these forts. However, original causeways also occur at both Cadder and Rough Castle – forts of ‘secondary’ status (Buchanan 1905: 455; Clarke 1933: 16). In an editorial comment, David Breeze reminded me that the digging of the Ditch, as a potential source of building materials, would usually have kept pace with, or slightly preceded, the construction of the Rampart (cf. Bidwell and Watson 1996: 33, for Hadrian’s Wall). Immediately west of Rough Castle, across the Rowantree Burn, the natural turf appears to have been sealed by the upcast mound, which is a strong pointer to the Ditch coming first in the local sequence (GAS 1899: 106: 112-13). Seeing that Rough Castle and Cadder were part of what is broadly believed to be the first construction sector taken in hand, it was always acknowledged that the ‘secondary’ plan must have come very early in the sequence (Hanson and Maxwell 1986: 134-35).
At Rough Castle, it is true, and probably at Cadder too, the stone foundation for the fort wall was found to abut the base of the Rampart (Buchanan 1905: 459 with fig. 7; Clarke 1933: 9-10), but a similar structural sequence is in evidence at the ‘primary’ fort of Mumrills (Steer 1961: 95). This is not surprising. The Antonine Wall tends to follow the edge of higher ground, so that it often sits on a slight slope to the north. This inclination is even stronger at fort sites, where space requirements or defensive considerations tended to push the north face to such edges. As a consequence, the rearside of the c. 5 m wide Rampart foundation often had to be terraced into a slope in order to have a secure and level bed, as Macdonald observed at Westerwood (1933: 281; cf. 1934: 220, 243 and 261 for Rough Castle, Castlecary and Croy Hill; Steer 1961: fig. 3, section C, for Mumrills). Now, with the rear kerb terraced into the slope, between 0.6 m and 0.9 m deep in places, there is a certain logic, structurally, to build up at least part of the superstructure before one starts constructing the fort ramparts which, at Westerwood, rested ‘on the natural surface’ (Macdonald 1933: 282). The result would be fort walls often sitting considerably higher than, and lapping up against, the base of the Antonine Wall Rampart – which is what we see at both ‘primary’ and ‘secondary’ forts (e.g. Mumrills and Westerwood).
At the northeast corner of Cadder the situation was more extreme, the ground level falling away ‘rather more than 1 in 5’ (Macdonald 1934: 302). Whether space limitations had pushed the fort corner to this steep slope, or a wish to have the latrine well-flushed, the consequence was a substruction unparalleled on the Antonine Wall. For the first 12 feet inside the fort corner, more or less coinciding with the latrine channel south of it, the Rampart had been terraced into the slope and built up with five courses of masonry on both faces and solid rubble in between; for the next 50 feet a unique hybrid solution had been adopted to overcome the slope (Clarke 1933: 10 with fig. 2). To Macdonald the situation was clear: at Cadder the Rampart had been built, and the causeway left undug, ‘with the needs of the fort in full view’ (1934: 302).3
This all rather detracts from the relevance of the documented junctions at Rough Castle. First of all, if Ditch-digging normally went hand in hand with Rampart-building, the implication of the causeway is that the builders of the length of Rampart that was to become the north wall of the fort knew about this installation. Unsurprisingly, the turf superstructure of Rampart and fort wall at the northeast corner, where the stone rafts of both lay level, appears to be continuous, to judge from the published photograph (Buchanan 1905: fig. 7; cf. Hanson and Maxwell 1986: 107). The picture of the northwest corner (Buchanan 1905: fig. 12), on the other hand, seems to show a somewhat irregular joint rather than a neat butt against a slightly inclined Rampart face like the few well-preserved ones on record (Macdonald 1934: pl. IX, XI.1 and fig. 21).
Such differences are no cause for great concern. The Roman army was used to breaking up, and delivering, linear works in short centurial segments, fort ramparts included (cf. RIB I 1818 and 1820 for
3 To Clarke, whose standard of excavation and reporting leave much to be desired, the latrine culvert through the Rampart
‘seemed to be definitely later’ (1933: 12). No substantiation is given other than that the cover-slabs included a perforated stone with signs of long use, which Clarke associated with an earlier Antonine occupation (although it is more likely to be prehistoric: Bill Hanson, pers. comm.). Clarke’s description of a second culvert through the fort’s north wall (1933: 11) leaves no doubt as to its secondary nature. This is unproblematic, as the fort’s drainage system was adjusted after the installation had been turned through 90 degrees while under construction, with construction of the north wall well underway (see below). The culvert of the inner east ditch was also clearly secondary (Clarke 1933: 14 with pl. V). Such outlets were not a standard feature of Antonine Wall forts. The culvert may have been inserted to fix a problem that had become apparent in a corner that must have been prone to stagnating water.
the building of Carvoran in 112-feet stints, just a few years before; and Hodgson 2017: 58, for a snapshot of discontinuous work on Hadrian’s Wall). A striking example of modular building is provided by Stone Wall milecastles 50-54, west of Birdoswald, which were constructed with their ramparts abutting the curtain wall, but clearly as part of one and the same building operation (Simpson and Richmond 1934:
144). Similar modularity is in evidence at Westerwood, where the work squads built two south corners of very different plan and happily varied between 4.3 m to 4.9 m when laying the foundation for the fort rampart (Macdonald 1933: 282). What we should be prepared for, then, is a potentially messy picture of centurial work crews doing and delivering their assigned jobs independently. At Rough Castle, the situation is further complicated by evidence for extensive reconstruction of the ramparts at a later stage, notably including the northwest corner (Macdonald 1933: 264-65).
Even small structures like fortlets can reveal modular building sequences. It is true that the stone bases of the ones explored are consistently bonded with the Rampart (Hanson and Maxwell 1986:
109). However, the last excavated fortlet, at Kinneil, illustrates just how disjointed the building process could be. At the northeast corner a line of kerb stones was found running part way across the stone raft for the Antonine Wall – apparently the end-point of a work stint (Bailey and Cannel 1996: 310 and 337 with figs. 3-4). From the published photograph it would appear that the western (rather than eastern) part, i.e. the north face of the fortlet, was built first, echoing milecastle 42 on Hadrian’s Wall. However, the line of kerbs does not align with the east face of the fortlet (as the butt joints of the curtain wall on both sides of Milecastle 42 do), but is sitting an awkward 1.5 m west of it. Moreover, the kerbed line strikingly coincides with a sudden narrowing of the Ditch from 11 to 6 m. So perhaps the more likely interpretation is to see this as the meeting-point of two work sectors, with the fortlet possibly shifted to this junction at a slightly later stage. Whichever scenario is preferred, the point is that the fortlet’s side wall may have been bonded with the Rampart/north wall subsequently (Bailey and Cannel 1996: 337). Evidence of this seems to be the curious discontinuity of the line of kerbs, the southern half apparently having been removed when the structure was bonded into existing Rampart fabric, whatever its state of completion at that point. All of this would probably have escaped the excavators had there not been the partially surviving line of kerbs across the stone base of the Antonine Wall.
No such pointer was found at Wilderness Plantation, but here, although the turf superstructure at the junctions appeared to be of one build, the kerbs of the fortlet rampart were found to be markedly different, and inferior, to those of the Antonine Wall (Wilkes 1974: 53), ‘a curious distinction if this masonry was dressed and laid in one go’ (Symonds 2018: 139).
We will later see that the picture of structural relations is further complicated by the overlooked phenomenon of fort wing-walls. For now it seems sufficient to cite the caveat given by Hanson and Maxwell: ‘Since it is unlikely that all the elements of the building process – the laying down of the Wall base, the construction of the turf superstructure, the digging of the ditch, the building of the Military Way – would have managed, or were even intended, to keep pace with each other, it is inevitable that some forts should demonstrate different relationships with different elements of the system’
(1986: 109). This, however, is to remove one of the cornerstones of the Gillam hypothesis and brings us actually very close to the traditional explanation of the ‘different relationships’ (Robertson 1979:
30-31).
The way forward, it is here proposed, is to analyse the Antonine Wall on a systemic level. Roman artificial frontiers (for an overview: Breeze 2011: 55-91) were highly complex systems combining
functions related to the control of movement, observation, alarm and military response. To this end, they typically employed running barriers, cordons of observation facilities, garrisons attuned to the local security situation, and frontier roads for lateral communication and scaling-up response.
Together these elements served as integrated infrastructures designed to support the army in its day-to-day security work along the edges of the Roman world. Some limites grew stagewise, with new
Together these elements served as integrated infrastructures designed to support the army in its day-to-day security work along the edges of the Roman world. Some limites grew stagewise, with new