A cashel is a ringfort built from dry-stone walling rather than earthen banks, and this one, if the surviving fragment is read correctly, would have formed part of a roughly circular enclosure somewhere in the region of 29 metres across. What survives measures about 2.4 metres in width, and it appears to represent the south-eastern sector of the original structure, the rest having been lost to the gradual reclamation and working of the surrounding pastureland.

Ringforts of this kind were built predominantly during the early medieval period in Ireland, roughly between the fifth and twelfth centuries, and served as enclosed farmsteads for individual family units. Cashels were particularly common in areas where stone was more readily available than the material needed for earthen raths. The Rathmore example sits in reclaimed pastureland, a landscape that has been steadily shaped and reshaped by agricultural use over centuries, which goes some way towards explaining why so little of the original enclosure has endured. The feature was identified locally as a possible fort, a detail that suggests the site had not been formally recorded before its inclusion in the 1999 Archaeological Inventory of County Galway, compiled by Olive Alcock, Kathy de hÓra, and Paul Gosling.