A cluster of three building platforms, side by side on the north-east facing slopes of Gelligaer Common, were identified and excavated in 1938. The excavations furnished dating material from the late thirteenth and early fourteenth centuries, for the first time placing sites like this in the medieval period. Although three were initially identified, a fourth platform has recently been noted nearby. Described from the east:
SO1139402919: terrace 15m long (NE-SW) with a width at the upper and lower ends of 5m and 4.3m respectively. The hood is 1m deep, terrace 0.75m high. The excavated interior is now grassy and uneven. Cultivation ridges surround the platform.
SO1138602935: central platform at a slightly lower level, the terrace measures 15m long (NE-SW) with widths of 7m and 5m at the upper and lower ends respectively. The hood is 1.5m deep, terrace 1.2m high. There is some evidence for the hood being slightly embanked. The platform interior is densely overgrown with rushes.
SO1138002955: terrace 12m long (NE-SW) with widths of 7m and 5.8m at upper and lower ends respectively. The slightly embanked hood is 1m deep, terrace 1.1m high.

All three platforms were excavated and found to have supported buildings. The north and south houses were simple rectangular structures. The central house was more complex and substantial, walls of turves and slabs 1m thick, a hearth at the hood end, opposing entrances in the long sides, and supporting uprights to carry the ridge pole of a thatched roof. The lower end was iregularly paved and there was an internal drainage gutter along base of the upper side walls. Evidence for metal working, including iron, was found. At the upper end broken pottery was trodden into the unpaved floor. The sherds, of coarseware and a glazed jug, provided a medieval date for the settlement.
No direct link between the buildings and adjacent cultivation ridges was detected during the excavations, though the ridges clearly respect the platforms. The settlement was interpreted as permanent rather than seasonal, though this is now debated as its ironworking is seen as unusual by some who favour seasonal use. The cultivation ridges are likely later in date.

SO1142102975: a fourth platform, seemingly missed in the 1930s, lies immediately below the three above. It is transected by a field wall. When viewed from above the platform hood appears to be a quarry scoop for wall stone. But when approached from below the outer end of the platform clearly projects from the wall. Smaller than its neighbours, it measures 12m long (NE-SW) and 5.5m wide at the outer end. The upper end of the terrace, less well defined due to damage through cattle trampling, is splayed out to about 6m wide. It is cut back to 1m deep and built out to 1.3m high.
Other platforms lie at a similar altitude to the south-east (see NPRNs 15320-3 & 305961-2; 421576).

Sources:
Fox, A., Archaeologia Cambrensis 94 (1939), 163-73 (No.5).
RCAHMW, 'Glamorgan Inventory. Medieval non-defensive secular monuments, PH36-45.
M.Locock, 'Deserted rural settlements in south-east Wales', in K.Roberts (ed.) Lost Farmsteads: Deserted Rural Settlement in Wales (2006), 51-5.
OS record card: SO10SW16.

David Leighton, RCAHMW, 20 April 2016