The natural drama of the drop did part of the defensive work; the rest was left to an impressive pair of earthen banks with a fosse, a deep cut ditch, running between them in a crescent shape that mirrors the shape of the headland itself. The outer bank has been disturbed by later field fences, but the inner one survives in remarkable condition, rising between 5.3 and 5.7 metres above the fosse floor and still imposing enough to make the logic of the site legible from the ground.

The dimensions give a sense of the effort involved. The fosse ranges from 3.4 to 4.5 metres deep across most of its width, shallowing slightly to around 3.2 metres at the south-east, where a causeway roughly 11 metres wide and over 25 metres long leads across to the fort's entrance. That entrance narrows to 3 metres at the inner bank, a bottleneck that would have concentrated any approach under close scrutiny. Inside, the enclosed area stretches 50 metres east to west and 36 metres north to south. Two internal mounds have attracted attention: one in the north sector measuring about 12 by 3.6 metres, and an oval mound immediately south of it at around 7 by 4.6 metres. Both may indicate the presence of a souterrain, an underground stone-lined passage used for storage or refuge, and the possibility is reinforced by an opening discernible at the cliff edge on the interior side of the outer bank, where exposed stonework suggests a further entrance or exit to such a passage. The 1841 Ordnance Survey map marks a 'cave' on the east side of the outer ring, which suggests the feature was noticed even then, though not fully understood. A second promontory fort, known as Stack's, occupies the southern side of the same headland, making this a rare coastal landscape with two such monuments in close proximity.