This fort is located on the high cliffs along the southern side of Inis Mór; it consisted of a promontory which was defended on the landward side by a curved terraced wall and a chevaux de frise. The remains of conjoined stone houses can be seen in the interior; a series of long rectangular buildings built along the western edge of the promontory may have been cattle byres in a later period. There are a large number of promontory forts along the west coast of Ireland and this type of fort is generally considered to be of Iron Age date (200 BC - 500 AD). A small amount of pottery recovered from the site suggests that there may have been some settlement here predating the defences we see today. The integration of the conjoined stone houses with a broad low platform on the inner face of the enclosing wall also suggests that Dúcathair was occupied down into the Early Medieval period (circa 900AD).