Palaeo-environmental data leave little doubt that arable agriculture was pursued extensively throughout the Iron Age in Scotland, variously witnessed by plant macro assemblages from excavated settlements and from wider-ranging pollen diagrams. In southern Scotland, at least, this latter source reveals episodes of massive forest clearance and expansion of arable indicators towards the end of the 1st millennium BC and through the early centuries of the 1st millennium AD (see section 3.2). Identifying the fields from which the pollen is derived, however, has proved more challenging, largely resting on the assumptions lying behind the identification of a handful of supposedly Romano-British or sub-Roman field-systems recorded in the County Inventories for the Border counties (RCAHMS 1956; 1967; 1978). It is small wonder that Stuart Piggott‘s Celtic Cowboys (1958) proved such an enduring explanation of Iron Age subsistence strategies in northern Britain.
Since the 1970s and Richard Feachem‘s (1973) summation of the work on upland field-system by the OS Archaeology Division, it has been clear that there are extensive traces of prehistoric agriculture across Highland Scotland, represented by scatters of small cairns and the occasional banks and lynchets. By the yardstick of ‘Celtic‘ field-systems, which have created an expectation that a field is a small plot of a quarter of an acre or so, bounded by lynchets and baulks, or reave systems with banks and walls taking in huge blocks of countryside (Fleming 1988; 2008), the Scottish field-system has always seemed incoherent and, to modern eyes, disorganised. What appear to be enclosed fields occasionally turn up, but examples of recognisable systems of bounded fields are so rare that they can only be presented as exceptions rather than as any norm. By way of example, Drumturn Burn in Perth and Kinross, with its trackway wending down between fields to a cluster of hut-circles often appears as a text book illustration of a Scottish field-system, and yet it is the only one of its kind amongst the dozens of hut-circle groups of North-east Perthshire. Another half dozen have a recurrent arrangement of banks in the immediate vicinity, but none of these define any areas or ‘fields’ as such. Similar commentaries could be made in Sutherland, for example, at Kilphedir and other hut-circle groups in the Strath of Kildonan (Fairhurst 1971b, Cowley 1998).
With the excavations on Arran in the late 1970s (Barber 1997) and more recently at Lairg (McCullagh and Tipping 1998), it has become equally clear that many of the hut-circle groups in Highland Scotland, and the scatters of clearance around them, are mainly Bronze Age in date, abandoned at the end of the 2nd millennium BC but often re-occupied to some extent in the late Iron Age, witnessed in Sutherland by the souterrains attached to some of the hut-circles. This work has also revealed that the remains around the hut-circle groups are routinely complex and multi-period, and even where it can be demonstrated that intense cultivation has taken place the field remains simply do not conform to tidy concepts of field-systems driven by southern English models. Essentially, the field-system of Iron Age Scotland is an untidy, cumulative and haphazard layout, , shaped on the one hand by topography and by the earlier remains within its compass, and on the other by the intensity and extent of the cultivation practices. Cumulatively through time the ongoing process of successive cultivations consumes its own history, and while relatively deep sediments may accumulate as a record of this history, trapped against an undisturbed baulk or an earlier boundary, dating the beginning of the process is as fraught with difficulty as dating its end. Field soils are by their very nature stirred and mixed contexts, and in Scotland rarely yield any cultural material that may assist in the establishment of a coarse chronology. As often as not the cessation of cultivation is conferred by a basal peat date and the assumption that the onset of peat growth followed the final season of cultivation in relatively short order (see Carter in McCullagh and Tipping 1998, 157).
The problem then, is by and large one of recognition, in that there is no single signature type of field-system that can be attributed to the Iron Age, though cord rig – a distinctively narrow type of cultivation rig first identified in the Border counties (Halliday 1982; Topping 1989; Halliday 1993) – was found beneath the peat around the hut-circles at Lairg, but while the abandonment of these particular rigs can be dated between AD 500 and AD 1200, and later still elsewhere (Carter 1994), it is more difficult to demonstrate their first usage in the north. In Northumberland they can be shown to be pre-Roman, occurring beneath the Roman forts of Rudchester, South Shields and Wallsend, while at Greenlea Lough an extant field-system with ridged field surfaces is overlain by a Roman temporary camp (Welfare and Swan 1995, 104-5). Elsewhere, across the Border counties traces of these ridged plots have been found adjacent to what are probably Early Iron Age settlements. In some cases they override individual buildings or part of a perimeter, but other than that they occur in topographical positions where other early remains have survived the ravages of medieval and post-medieval cultivation, thus confirming a relatively early landscape context. These plots are not only undated, but probably undatable. As the discoveries at Lairg, and indeed on Arran, show, the concentration of examples of cord rig in the Border counties is a visibility issue – the slightest growth of peat tends to fill the furrows and quickly renders them invisible on the ground or from the air.
In itself, Cord Rig is not the solution to the problem. Nevertheless, the character of the plots is revealing, for they are often very small and were probably little more than gardens. In some cases a smoothed area can be detected beyond the limits of the ridging. The ridged area, it seems, is merely the last season of cultivation in a plot which has constantly changed shape and extent. If there were ever enclosures, they were no more than temporary fences, and the lack of replication of the boundaries from year to year has prevented the formation of lynchets or other recognisable boundaries. These fields are simply pieces of ground set aside for cultivation or pasture. This sort of dynamic and constantly changing pattern of cultivation is perhaps embedded in the major untapped source of Iron Age field-systems that almost certainly hide in the deepened soils that are found throughout the Northern Isles and in machair deposits in the Western Isles. Almost invariably recultivated and further deepened in more recent periods, many of these probably contain deep Iron Age field soils. Unfortunately these tend to be examined and sampled vertically by trenches and boreholes; no individual plots within such a deposit have been delineated, and no junctions between plots have been recorded. Herein lies a huge untapped potential to explore and understand the detail of arable production in the far north and north-west, while it has yet to be tested whether similar deposits may be found on the mainland further south.
The application of soil science to these Atlantic-zone deep soils has produced remarkable insights into the creation of plaggen soils, deliberately deepened and fertilised, which were then curated as a valuable resource (Guttmann et al. 2004, 2006, 2008). This pioneering work merits wider application. While such questions are far harder to answer in the plough-affected lands which characterise other parts of the country, it is possible that similar evidence could be found stratified in alluvial sequences.
It remains to comment on the handful of field-systems in the Border counties that are traditionally held to be Romano-British or sub-Roman. They remain undated, though one on Ellershie Hill in Lanarkshire is notable for the unenclosed house platform cut into the leading edge of one of lynchets. This field-system is almost certainly Bronze Age, as is the Stan Hope system in Peeblesshire. Others are perhaps late Iron Age, the best preserved being one including a series of long strip fields partly covered with cord rig on Hut Knowe, Roxburghshire. This occurs in part of the Cheviots with one of the highest concentrations of cultivation terraces to be found anywhere in the Borders. Cultivation terraces embrace a wide range of lynchets, some of which are short and scrappy, and others long and sinuous, these latter often emanating out of systems of reverse-S rig and furrow (see discussion in RCAHMS 1997, 40-43). Yet others are wide-spaced, effectively forming long strip fields which have been almost invariably subsumed into later rig-systems, whose furrows can be detected cutting obliquely along them or over the lynchets. Dating the origin and evolution of these flights of terraces is long overdue, as is the testing of their relationships to nearby settlements.