1994:233 - RATHDOWN CASTLE, Rathdown Upper, Wicklow

|Archaeological test trenching along a portion of a proposed sewage pipeline which forms part of the Greystones Sewerage Scheme, Stage 2, Phase 2 took place in mid-1994. The pipeline runs northwards from Greystones to the old sewage treatment works site at the end of Grove Lane in the townland of Rathdown Lower which is to be decomissioned as part of the new sewerage scheme.

The archaeological potential of the site has long been recognised in the archaeological and historical record, and the area tested occurs within a large area of archaeological interest, considered to include extensive remains of medieval settlement. The archaeological area stretches from the site of the castle of Rathdown (now the old sewage treatment works site), westwards along both sides of Grove Lane and embracing the church site of St Crispin’s Cell. The area is characterised by numerous, and varied, sub-surface features, many of which can be identified on the ground. The area has also been studied in detail from the air (Reports by Leo Swan 1991) and was scheduled by the Office of Public Works and entered in the Register of Historic Monuments in 1992. The scheduled area includes the church site and extends eastwards as far as the site of the castle. It includes the fields on the south side of Grove Lane in which numerous sub-surface archaeological features are evident. For some unaccountable reason the scheduled area does not include the field to the north of the castle in which the clearly visible remains of a moated enclosure are located, along with other sub-surface features (St Joseph, BDP 25). The main features visible are: two raised rectangular platforms, of unknown derivation and date, to the west of the pipeline corridor; the remains of a ‘mill race’ (tail race?) which runs eastwards through the site and is crossed by the pipeline corridor, two linear features running north–south to the east of the platforms and two systems of lazy-bed cultivation which lie to the east of the pipeline.

The sewage pipeline corridor runs through the field to the west of the castle site and present sewage treatment works crossing the remains of a supposed ‘mill race’ (tail race?) and other features of apparently agricultural derivation. The archaeological test trenching was undertaken to assess the area crossed by the pipeline corridor to ensure that no features of archaeological interest would be damaged during the pipe-laying process. An alternative, but less practical, route had been considered and was available should the necessity arise.

The pipeline ‘corridor’ was tested in a grid of 10–12m long, mechanically excavated slit trenches. The trenches were set 5–10m apart and arranged in groups running both east-west and north-south. This arrangement has been found to be most effective in testing linear areas such as pipeline corridors. The 5m spacing ensures that significant small features of interest are unlikely to be missed and the change in orientation ensures that linear features are not crossed obliquely.

The results of the assessment indicate that the pipeline crosses a relatively marginal area of archaeological activity, with some features dating back to the medieval period and some of obviously more recent date. Most of the features revealed have an agricultural derivation and some of the features certainly appear to date to the medieval period, i.e. during the occupancy of the castle and surrounding settlement.

To the south of the ‘mill race’ was a spread of burnt soil which was impossible to interpret or date with no associated features and no dateable finds. The ‘mill-race’ produced disappointing results from an archaeological viewpoint, but it was clear that the pipeline ran through a portion of this feature which displays no evidence for archaeological activity, and monitoring of the pipeline construction confirmed this.

The sewage treatment plant, at present in working order, was built in 1975, and, with the new sewerage scheme, is due to be decomissioned. The site on which it was built possessed the recorded, scant and ruinous remains of a portion of the late 13th to early 14th-century castle of Rathdown.

During construction of the treatment works, which involved extensive excavation for the insertion of tanks and a comprehensive re-grading of the site, archaeologically sensitive material and soils as they cross the line were removed. Some of the remains of the structure recorded in 1972 and the supposed line of the ditch on the west and south side of the moated enclosure were also removed along with the remains of a later lime kiln. Nothing can now be seen of the archaeological remains on the site but sub-surface remains have survived in places. The decommissioning and landscaping of the site will not involve further deep excavation.

An oblique aerial photograph of the site, taken by J.K.S. St Joseph of Cambridge University in the late 1960s, provides the basis for the present interpretation of the remains. On this print the remains of a clearly defined moated site are obvious. These encompass the site of the treatment works, showing the remains of the lime kiln and extend to the north of the laneway. The masonry recorded in the 1972 inspection of the site lay in the south-west corner of the moated enclosure. Archaeological assessment of the proposed new works involved the opening and inspection of four test trenches which revealed ephemeral traces of archaeological deposits as follows:

1) At the extreme north of the site the most ephemeral remains of masonry structures, in the form of blocky stones and mortar, were noted in humic soil at a depth of 0.4m below ground level at the north of the trench.

2) Running north-south, the scant remains of the base of the main enclosure ditch still survives some 19–23m to the east of the western perimeter fence (in the area tested); the remains of the outer ditch are likely to have been removed during the excavation for the surface water-drain just inside the fence-line.

3) The southern line of the ditch underlies the present building, inspection chamber, roadway and northern disposal tanks. Excavation for the rising main which runs east-west across the site will have almost certainly caused further disturbance to the southern side of the enclosure ditch. Some remains of it may exist, however, just to the north of the rising main.

There are no plans for a further reduction in ground levels on the site, but it has been recommended that any proposed alteration to the existing surfaces for landscaping purposes should be carried out under archaeological supervision. It has also been recommended that a drawing of the proposed landscaping and planting should be examined by a qualified archaeologist before the planting scheme is finalised, and that there should be no attempt to extract by excavation the foundations of the existing structures on the site.

Rath House, Ferndale Rd, Rathmichael, Co. Dublin