A rath is a circular earthwork enclosure, typically dating from the early medieval period, that once served as a defended farmstead or the residence of a person of some local standing. This one sits in low-lying pasture in Ballinlag, on a gentle rise above a stream valley in County Mayo, its form now barely legible at ground level.

The enclosure measures roughly 24.5 metres north to south and 25.5 metres east to west, and its circular shape was already clearly recorded on the Ordnance Survey six-inch map of 1838. By the 1931 edition, the same map was describing it as an irregular, subcircular form incorporated into field boundaries, which tells its own story about how the site had been treated in the intervening decades. What remains today is fragmentary: on the eastern half, an intermittent earth and stone bank survives to only about 0.3 to 0.4 metres in height, while the south-western arc has been adapted and built up to serve as a field fence, reaching between one and 1.2 metres on its exterior face. The north-western arc has been cut through entirely by a straight field boundary. Inside the enclosure, a low spine of raised ground runs on a north-west to south-east axis, with the ground falling away more steeply to the west. A possible gap at the south-east may mark where the original entrance once stood. Just 140 metres to the north-east, a second rath sits on a ridge overlooking this one, suggesting the area was once more densely settled than its present quiet pasture would imply. Ash trees have taken hold along the south-eastern perimeter, and hawthorn, blackthorn, and brambles have colonised the western half, giving the surviving earthworks a modest but distinct presence in the field.