A building platform is located on the north-east facing slopes of Gelligaer Common, above the Darran valley. The platform terrace measures 8.5m long (north by south) by 6m wide, cut back to form a hood is 0.9m deep, the terrace built out to 0.75m high. The turf-covered interior slopes gently to the north, and there is a possible step-down roughly half-way along the terrace. Both hood and terrace (lower end) are slightly embanked.
This is possibly the platform described by Fox as 'unfinished'.
Additional sources:
A.Fox, Archaeologia Cambrensis 94 (1939), 180 & 194.
OS record card: SO10SW26.
RCAHMW, Glamorgan Inventory vol.3 part 2 (1982), 30.
RCAHMW air photos: 945106/51, 53.

David Leighton, RCAHMW, 11 May 2016