2019:723 - St Joseph's, Clonsilla, Dublin 15, Dublin

Archaeological monitoring at Clonsilla in 2019 exposed the remains of a medieval field system and a very unusual feature: rows of pits in one of the medieval fields. Each pit was identical (1.6m by 0.5m and 0.35m deep), and arranged in rows 6m apart, with each pit 6m from each other pit. The pits rows extended over an area measuring at least 80m by 50m. The pits contained few artefacts other than small sherds of medieval pottery.

This feature is very different from the well-known pitfields of County Roscommon. Despite this, the Clonsilla features share many characteristics of the pitfield monument class and can be considered to form part of this monument category. This is the first time a pitfield has been identified in Dublin.

The Clonsilla pit alignments appears to be restricted to a single medieval field (or part of a field) measuring 100m by 70m and defined by ditches to the north and south. The field would have contained approximately 100 pits. Although no medieval pottery was found in these particular ditches, similar ditches that appear to be part of the overall field system to the east contained medieval pottery. The eastern extent of the pitfield was not defined by any visible boundary, so it either extended over only part of a medieval field, or else the eastern boundary of the field was defined by an archaeologically-invisible line such as a shallow drain, fence or hedge. The western edge of the pitfield was not identified. The regularity of the pits within the pitfield certainly suggest that the full c. 7,000m2 extent of the feature formed a single land parcel without internal subdivisions or obstructions.

Considering the consistency of pit alignment, form and backfill, the pits should be considered a single-period planned project rather than the result of a gradual construction over time. Based on the breakdown of pit alignment from north to south, it is suggested that the pitfield was laid out from north (uphill) to south (downhill) by a team of pit-diggers spread out 6m apart and excavating pits roughly every 6m. The only other archaeological feature within the pitfield was a scorched pit, which was situated between a group of pitfield pits, and which contained bone. Bone found in two adjacent pitfield pits suggests the scorched feature was contemporary, and it may represent a location for the cooking of a working lunch. It is unclear if the pits silted up naturally over time after they were dug, or if they were backfilled relatively rapidly. The latter seems more likely, since the regularity in pit profile and in pit rim form would have become distorted if they had been left open for a sustained period of time. The regularity of the pit fills, and the distinct difference between the pit fills and the underlying natural subsoil, may also point to deliberate backfilling rather than gradual accumulation of soil.

Various explanations were explored (natural, soil mending, quarries, collecting water, storing potatoes, drainage, flax pits, damaging fields, producing lime, structural, test-pits, leisure, planting pits, military) and none was found to be convincing. The Clonsilla pitfield is an enigmatic medieval landscape feature.

Archaeology Plan, 32 Fitzwilliam Place Dublin 2