The earthwork known as Rathardan sits on a gentle rise in undulating pasture near Ballysakeery, looking east over the estuary of the River Moy. It is a rath, the most common type of early medieval enclosure in Ireland, typically a circular area defined by one or more earthen banks and ditches that once enclosed a farmstead or the residence of a person of local standing. Here the defining bank survives best along the southern arc, where it still stands about 1.8 metres on its outer face and nearly four metres wide; elsewhere around the circuit it has been reduced to a stony earthen scarp, its outward slope sharpened by the natural fall of the knoll itself. Two gaps punctuate the perimeter, one at the north-north-west and one at the south-east, but neither can be confidently identified as the original entrance.

The rath has carried its name for at least as long as maps have recorded it. It appears as 'Rathardan' on Ordnance Survey six-inch sheets from both 1838 and 1929, suggesting it remained a recognisable landmark in the landscape across that span of time. Inside the enclosure, which measures roughly 26 metres east to west, there is a further slightly raised sub-circular area, defined by its own internal scarp on the north, east, and south sides. On its south-eastern edge, a two-metre gap leads into a shallow circular hollow about four metres across. Whether this depression is the ghost of an early structure built when the rath was in use, or simply the scar of more recent digging, is not clear. That ambiguity is part of what makes the site interesting: the ground holds a question it has not yet answered. The wider setting adds another layer of curiosity. Two further raths are visible from the knoll, one roughly 300 metres to the south-east and another about 450 metres to the north-east, suggesting this part of the Mayo countryside was once more densely settled and organised than the present quiet fields might imply. Gorse and blackthorn have crept across the southern half of the perimeter, softening its edges into the ordinary texture of the hedgerow.