Most of Scotland’s souterrains are thought to date from the last centuries BC and early centuries AD, although exceptionally their use is also known into the second half of the 1st millennium AD (Watkins and Barclay 1981; Armit 2000; Halliday 2006). Commonly found juxtaposed and in some cases associated with other settlement evidence, such as roundhouses or enclosures, the majority of the nearly 200 examples in the area are concentrated in the eastern lowlands. The vast majority are known as cropmarks, which are found in areas where well-drained soils coincide with arable cropping over the second half of the 20th century. However, there is no simple relationship between the distributions of known souterrains and cropmarks, given that some areas of dense cropmarks apparently do not include any examples. This hints that the use of souterrains may have varied locally and regionally. Fewer souterrains occur as earthworks, and areas with poorly drained soils that are not conducive to cropmarks or are set to pasture are poorly understood.
Excavation in 1977 at Newmill East (MPK2309) near Bankfoot significantly advanced Scottish souterrain studies, confirming that at least some were accessed from house interiors. It was associated with an unenclosed settlement of the later Iron Age and was probably built in the 1st century BC but with continued activity into the early centuries AD (Watkins and Barclay 1981). It not only confirms that open settlement continued through this period but also offers a chronological proxy for the region’s unexcavated souterrains identified in association with isolated or clustered unenclosed roundhouses (Wainwright 1963; RCAHMS 1994, 63–68; Armit 1999). Similarly, another large example, excavated at Shanzie Farm, Alyth, may well have been associated with settlement as early as the 3rd century BC but with activity as late as the 4th century AD (MPK12170; Coleman and Fraser 2002, 97).
More recently, developer-led work has contributed significantly through the discovery of two well-preserved examples, associated with a late prehistoric settlement at Loak Farm (MPK20126; Kirby 2019) and Northleys near Luncarty (MPK20138; Paton and Wilson 2019, 14–15). Northleys has at least two phases of construction, including an extension in length and a possible timber lining or superstructure. The post-excavation analysis (Wilson and Clarke 2019) illustrates how advances in dating (eg Bayesian statistical analysis) and palaeoenvironmental analyses, including soil micromorphology, are increasing the potential to make major improvements to the understanding of the site type. They therefore contribute to the national narrative of these enigmatic structures.