The one at Corbally in County Mayo does not appear on any edition of those maps at all, which raises the quiet question of whether it was already so reduced by the time the surveyors passed through that they simply missed it, or whether it slipped past them for some other reason entirely. A rath, to give the term its proper meaning, is a roughly circular or oval earthen enclosure, typically defined by a bank and outer ditch, that served as a farmstead or settlement during the early medieval period. The Corbally example belongs to that category in outline only; what survives has been levelled almost to nothing.

What remains is a slightly raised oval area measuring approximately 23.5 metres on its northeast to southwest axis and 32.8 metres across from northwest to southeast. Along one arc, between the southwest and north-northeast, the ground rises just enough to suggest where a bank once stood. On the north-northeast to south-southeast side, a low scarp survives more clearly, around half a metre high and roughly a metre and a half wide, with large stones visible within it and the natural fall of the ground lending it a little extra definition. To the south and southwest, the enclosing element has vanished entirely. A shallow depression just outside the western scarp may be the remnant of a fosse, the ditch that would originally have accompanied the bank. Inside the enclosure, a modern post-and-wire field fence cuts across the interior, and a row of large stones running parallel to it in the southeastern quarter may represent an older field wall that the fence replaced. A slight hollow in the northern interior adds one more ambiguous feature to a site that has been thoroughly reabsorbed into the working farmland around it.

The rath sits in improved pasture on gently rising ground, with open views stretching most extensively to the east and south-southwest. The landscape reads as ordinary agricultural land now, and without prior knowledge there is almost nothing to announce that the slight unevenness underfoot was once a deliberately constructed enclosure where someone, more than a thousand years ago, built a life.