1994:092 - FINGLAS BY-PASS, Dublin

The archaeological testing by trial-trenching of the proposed Finglas By-pass was undertaken by Archaeological Development Services Ltd. for Dublin Corporation. It was the second part of the archaeological assessment for the site, a geophysical survey having already been carried out by ADS in association with Geoquest.

The site, which covers an area north and south of Mellowes Rd., Finglas, lies within an area of archaeological potential and includes the corridor through which the suggested line of the monastic enclosure ditch is thought to pass. The geophysical survey carried out on the site was unsuccessful in locating the postulated line of the enclosure due, perhaps, to the unusual amount of overburden on the site which would effectively mask any archaeological features.

Two other interesting areas were, however, identified by the results from the geophysical survey. The first of these to the north of Mellowes Rd. consisted of a 5m wide band of high resistance anomalies which indicated a positive feature running east-west across the survey area. Cartographic sources suggested this feature to be the line of a track-way branching off to the west of the old Watery Lane and testing proved this to be the case.

To the south of Mellowes Rd., a rectangular feature running parallel and some 30m distant from the road itself was discovered. This feature measured at least 50m east-west with an apparent return to the north at the east end measuring some 20m. There was no evidence for any known structure here and since the resistivity meter used on the survey could not see below 1m and the test-bores indicated that up to 7m of made ground exists in this area, it was felt that the feature was quite recent. Testing proved this to be the remains of a hard standing, probably laid down during the construction of Mellowes Rd.

In all three trenches were opened, two as outlined above, with a third across the area through which the suggested line of the monastic enclosure passes. This trench was positioned so as to cross the proposed line of the enclosure as suggested by Swan. Geotechnicial bore holes and test pits dug in the area revealed there was up to 3.5m of redeposited fill, dumped in the area to make up the level of the ground prior to the construction of Mellowes Rd.

The excavation of Trench 1, ground level 58.5m OD, was carried out using an Atlas mechanical digger, with a 3ft wide toothed bucket. The trench measured 2m wide and 21m in overall length, with the projected line of the enclosure running through the northern end. At its deepest, the trench was over 5m in depth, with ground water seepage at 2m.

The trench revealed a substantial ditch with an associated bank to the south. The ditch measured some 8m wide and at best 2m deep with the bank measuring 7m in width and standing at best 0.5m high. The ditch was apparently partly rock-cut with the excavated material dumped on the south side to form the bank. The formal stone facing uncovered in the section is puzzling. It was undoubtedly part of the fill of the ditch and most likely marked its northern extent at some stage in its use. However, due to the fact that the primary cut on the northern side of the ditch was not rock cut, the exact extent of the ditch was evidenced in subtle changes in boulder clay morphology, the nature of which were not precisely discernible looking down a 5m deep excavation trench. Nonetheless it was reasonably clear that the soils at the north end of the trench consisted of undisturbed boulder clay while it was equally clear that the formal stone facing had been set into redeposited fill. It is therefore almost certainly the case that the northern limit of the ditch lay between these two points.

The discovery of this ditch in roughly the place where it had been postulated by Swan was significant as it may mark the northern extent of the monastic enclosure of Finglas. However, the OS 6" maps of 1844, 1909 and 1936 record a townland boundary crossing the area at this point. Indeed it was this boundary which Swan originally pointed out could mirror the line of the earlier monastic enclosure. No dating evidence was recovered during the testing save only for a number of post-medieval sherds of pottery from non-ditch contexts and therefore it is possible that the ditch is simply a substantial townland boundary. Nonetheless, the size of the primary ditch, some 8m wide x 2m deep, with a 7m wide bank in association, suggested a boundary marker of greater significance than delimiting a townland. Indeed the presence of the mortared stone face, apparently re-cut into the fill of the ditch, may represent the re-use of the ditch as such a boundary. The test trench results suggested, albeit tentatively, that there were at least two phases represented in the section, the later reflecting the use of the ditch as a townland boundary with the primary ditch and bank marking the line of the monastic enclosure. On foot of these results an excavation was proposed in the area to the west and east of the river to examine in plan the form and line of the ditch.

1. L. Swan, 'Monastic proto-towns in early medieval Ireland: The evidence of aerial photography, plan analysis and survey', p. 91

Fig. 4.11; in H.B. Clarke and A. Simms (eds.) The comparative history of urban origins in non-Roman Europe. British Archaeological Reports, Oxford, 1985.

Powerhouse, Pigeon House Harbour, Dublin 2