Oystermouth Castle Community Dig


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Project background

The City and County of Swansea maintain Oystermouth Castle as a visitor attraction. The castle is both a Scheduled Ancient Monument and a Grade I Listed Building. Visitor services to the site are provided by the Friends of Oystermouth Castle, an active volunteer group. Following the results of a geophysical survey commissioned by the Friends, a research design, to include survey and archaeological excavation, was proposed by GGAT to elucidate the nature of the geophysical anomalies. The key element of the fieldwork relies heavily on the active participation from the local community who will receive training in aspects of archaeological excavation.

The geophysical survey

The castle buildings occupy a spur on the southern side of an amphitheatre-like public park on the hillside directly overlooking the sea, which lies to the east; this spur continues southwest of the gatehouse, where it is known as The Knoll. There is another, saddle-shaped ridge to the east, with a mound known as Castle Tump on its southern summit. The bowl-like area between the two ridges is known as The Green.

A programme of geophysical survey was carried out for the Friends of Oystermouth Castle. This examined four areas in, respectively, the inner courtyard, the exterior of the gatehouse and The Knoll, The Green and Castle Tump.

The results from the inner courtyard were disappointing, and will not be discussed further as this area will not be available for the proposed excavation. Variable results were produced from the other areas. None of the features noted by magnetometry seemed likely to be of archaeological origin, so the features in the following three areas were all located on the resistivity survey. The outer wall of the exterior of the western drum tower of the gatehouse was clearly imaged as a low-resistance anomaly bordering a semi-circular high resistance anomaly, probably representing a rock-cut foundation trench around a mass of rubble. What appeared to be its counterpart on the east was seen during a watching brief on the cable-trenches when the floodlighting was installed. A low-resistance anomaly on the far side probably represents the ditch separating the gatehouse from the rest of the knoll, which probably served as a barbican. A couple of high resistance anomalies on the Knoll might represent buildings or piles of rubble, whilst a linear feature running parallel with it and to the east may represent a wall or track.

Results on the Green were disappointing, probably due to the poor weather conditions. The only features that were imaged were probable modern cultivation marks. On the Castle Tump ridge it proved difficult to distinguish whether the features imaged by resistivity were archaeological or geological in origin. The best candidate as archaeological features is a sub-oval area of high resistance of the northern summit, because of its regularity. Map regression carried out as part of the study also identified a medieval dovecot, shown on an 1802 map of properties belonging to the Beaufort estate. However, this was not picked up on the survey, possibly because it did not cover the relevant area.


The masonry structure of the castle has been studied in detail by the Royal Commission of Ancient Historic Monuments Wales , but the exterior of the castle is less well understood. The RCAHMW account limits mention of the surrounding earthworks to a paragraph on the area to the north, interpreted here as probably being the earth and timber castle and its presumed bailey. However, it does not describe them. No other part of the surroundings of the castle has been the subject of a detailed topographic survey. Geophysical survey has provided some information as to possible structures outside the castle, but only archaeological excavation would provide definite evidence.

There were three areas in particular where excavation would be particularly useful:

  • The area to the south of the eastern tower wall of the gatehouse (the Knoll). Excavation could help to resolve the question of the construction status of the tower, and ascertain whether the ditch that appears to be shown in the geophysical survey can be located. Further south on the knoll, a possible wall and possible area of structural debris were located. The Knoll has also produced a parchmark, and there is a section of possible wall further south
  • The earthworks to the north of the castle, presumed by RCAHMW to be the defences of the outer bailey, but as a possible quarry by Davies. Excavation would determine which of these is correct.
  • The Castle Tump ridge. This has also produced possible areas of archaeological origin on its northern and southern summits.

However because the castle surroundings are a public place, the council requires that all excavation over 0.15m (6") in depth should be enclosed within security fences. For this reason it has been decided that excavation should concentrate on a single area, to minimise cost and disruption. The easiest area to fence will be the Knoll, where existing boundaries can be utilised, and where there is the most certain prospect of positive archaeological results and therefore of public engagement. We therefore propose to survey the open area surrounding the castle and excavate three trenches on the Knoll, one to examine the gatehouse and ditch, and the others to examine features identified by geophysical survey on the Knoll.