The range of recurring ground-plans of timber roundhouses in much of southern and eastern Scotland are often known by short-hand reference to their salient structural feature as of post-ring, ring-groove, and ring-ditch construction (see Dunwell 2007; Harding 2023 for a summary). The broad distinctions have merit, but the structural features are not exclusive: buildings with a ring-groove wall regularly have an internal post-ring providing the main structural support, while ring-ditch houses always have a post-ring and sometimes have a ring-groove wall; post-rings alone may have had a turf wall, but could also have lost any ring groove to erosion. Further, there is even doubt whether some structures (for example ring-ditch houses) acted solely as domestic houses. It is now accepted that post-rings, ring-grooves and related construction techniques cannot be regarded as culturally or chronologically diagnostic, which would be especially true of ring-ditches if they are the consequence of usage rather than design.
Post-Ring
For many years the popular assumption was that Iron Age houses were circular with post-ring walls of wattle and daub, with thatched roofs supported by a central post on the bell-tent principle. It appears that by the Iron Age central post support was superseded by double-ring roundhouse in which roofs were supported by a main weight-bearing post-ring. Examples are known from a variety of recent excavations including Dryburn Bridge (Dunwell 2007).
Ring-Groove
Ring-groove houses are characterised by having a groove type of wall foundation, generally not invariably of an outer wall. Similar in appearance are the drainage gullies thought to have carried away water from the eaves. It is usual to infer that the ring-groove was the foundation of an upright wall, commonly of planks or split timbers. Five houses of ring-groove were identified and excavated at Broxmouth, East Lothian (Hill 1982; Armit and McKenzie 2013), of which two – Houses 2 and 3 – were reasonably intact. Houses 2 and 8 were dated to Phase 6 of the site, that is 100BC to AD210. That late dating of ring-groove houses from Broxmouth was unexpected but does accord with accumulating evidence for the use of ring-grooves in Late Iron Age structures in Angus and Stirlingshire.
Intriguingly, at least at Broxmouth, the roundhouses were kept scrupulously clean, and there is little evidence for artefactual material or faunal remains. Instead the finds that were recovered appear to have been deliberately placed, either being recycled as building materials or as structured deposits (Armit and McKenzie 2013). Such special deposits associated with the construction, abandonment and modification of buildings are not uncommon in British Iron Age contexts.
Ring-Ditch
Until a few decades ago ring-ditch houses were often regarded as a phenomenon of the Scottish Borders but they are now known from eastern Scotland and as far as the Moray Firth and with antecedents dating to the Middle Bronze Age. There is much debate as to whether the ring-ditch is seen as structural or simply the product of erosion. On many sites (such as Broxmouth and Dryburn Bridge) the ring-groove hollow is filled with stones or paving, suggesting an attempt to inhibit further erosion, and perhaps to ensure effective drainage.
Numerous ring-ditch roundhouses have been excavated across the region, for example, Braidwood, Midlothian (Stevenson 1949), Broxmouth (Armit & MacKenzie 2013) and Dryburn Bridge (Dunwell 2007). Excavations at Braidwood enclosure in Midlothian revealed evidence of at least 16 houses mostly ring-ditch, most of which are believed to have been constructed during the second phase of occupation as several of them overlie the earlier palisade. In the pre-radiocarbon era it was thought that the occupational period of the settlement in the Iron Age would have been from the pre-Roman Iron Age to 100-200 AD. Evidence from Broxmouth and Dryburn bridge demonstrate that ring-ditch houses, at least at these sites, should be assigned to the earlier and middle centuries of the 1st millennium BC.