This site, which was identified via cropmarks which were revealed on aerial photographs, is a promontory fort located on the edge of precipitous cliffs.
Four concentric curving ditches measuring around 100m long, and each around 3m wide, cut off the headland and enclose an area of around 100m from north-west to south-east by a maximum of 75m across.
On the north-east side, around 20m south-west of the edge of the cliff, is an entrance causeway which breaks through all four ditches. There may have been a palisade within the innermost ditch at the entrance, and a further palisade between the innermost ditch and its nearest neighbour.
In the 12th century Greenan Castle was built within the fort.