1994:102 - ST MAELRUAN'S, Tallaght, Dublin

Following trench monitoring carried out on this site throughout the recent developments, a small-scale excavation was carried out to investigate the two ditches which enclose a graveyard and overlying medieval archaeology. By the time a crew had arrived on site, the developer had already scarped the site by up to 0.5m–0.75m. This effectively removed all overlying archaeology and also truncated both ditches. There was no indication of an outer bank and the inner bank was only partially investigated.

Three trenches were opened up along the south-west quadrant of the enclosure and these were limited in their extent by existing ground work. The inner ditch as excavated measured up to 6m wide by 4m deep. It was steep sided with a stepped inner edge and a fairly wide, flat bottom. The lower fill was a series of laminated silty clays which filled the ditch by up to 1m. There then followed a period of mixed activity in which the ditch silted up from dumped material and was periodically cleaned out. No turf lines were observed, suggesting that the ditch was in continuous use. Several sherds of medieval pottery—13th/14th century—were extracted from the lower fills of the dumped deposits. By the end of the 14th century the ditch was deliberately filled in and levelled. An 18th-century stone-lined drain cut across the upper fill in one trench and 19th-century cultivation furrows were evident in two of the trenches. No pottery was found from the primary silty fill. The inner bank had been built up from a series of sterile deposits which had been dumped on top of natural boulder clay. No finds were recovered from the bank.

The outer ditch was severely truncated and damaged by the recent insertion of sewage pipes and connecting manholes. It was very irregular in profile and varied throughout the three trenches. As excavated, it survived to 3m wide and 2.2m deep. The distance between the two ditches varied from 3m–6m, suggesting that the two were not exactly concentric. In all three trenches the outer ditch had a similiar fill of stony, grey, dumped, clayey deposits. It had also undergone a series of backfilling and recutting. Some medieval pottery was recovered from the upper fill of one trench and from an unsecure deposit from another. Overall the fill proved to be fairly sterile. One trench produced overlying archaeology of a clay-lined pit containing timbers charred in situ. Overlying this was a mortary deposit which suggests that the pit may have been involved in the process of lime mortar. Its total extent could not be determined as it had been truncated by recent scarping. There was no evidence of an outer bank or palisade.

From historical sources we know that the monastery was founded between AD 766 - 792. The inner diameter of the inner enclosure gives an estimate of c. 130m. The inner ditch was clearly defensive and the outer ditch was constructed to support it at a later date. As yet a C14 date has not been obtained for the primary fill of the inner ditch. Should the date be early Christian then the inner ditch must have been constructed contemporary with the early monastery. If, however, a date of pre-Christian Iron Age is obtained, then the ditch must have originally been secular and perhaps indicates the boundary of a small kingdom.

Powerhouse, Pigeon House Harbour, Dublin 2