Originally classified as cairn 'Z' by antiquarian George Conwell in the 1860s, who believed it to be part of the ancient Slieve na Calliagh complex, modern archaeological surveys suggest this feature is actually a medieval motte; a type of fortification introduced to Ireland by the Anglo-Normans in the 12th century.

The mound rises between five and seven metres high, with a flat grassy summit measuring 12 metres across and a base spanning 35 metres in diameter. A defensive ditch, or fosse, curves around the uphill side of the structure from southeast through west to north, with remnants of an outer bank still visible at the northwestern edge. The summit shows signs of quarrying, and it appears that excavated material was dumped into the northwestern section of the fosse at some point in its history.

To the southeast, faint traces suggest the presence of a bailey; the enclosed courtyard that typically accompanied these timber castle structures. This rectangular area, measuring roughly 31 metres from east-northeast to west-southwest and 24 metres from north-northwest to south-southeast, would have served as the main living and working space for the castle's inhabitants. A slight rise along the south-southeastern edge may mark the remains of a defensive bank that once protected this lower enclosure.