The rath at Largan measures roughly 40 metres north to south and 31 metres east to west, and what distinguishes it from many of its kind is the quality of its preservation: two banks survive in good condition, separated by a fosse, the term for the defensive ditch dug between or around the raised earthen walls of such an enclosure. The causewayed entrance faces south-southeast, where the fosse is bridged to allow access, a feature common to ringforts but not always so clearly legible in the field after centuries of weather and agriculture.

Ringforts are among the most numerous monument types in Ireland, with estimates running into the tens of thousands across the island. Most date broadly from the early medieval period, roughly the fifth to the twelfth centuries, and served as enclosed farmsteads for individual family units, combining domestic space with protection for livestock. What gives the Largan example an additional layer of interest are the two short parallel banks, each about three metres long, that project outward from the outer bank at right angles, one pointing NNE and one NNW. These are interpreted as possibly part of an annexe, a secondary enclosure attached to the main rath, which might have housed animals, stored goods, or served some other ancillary function. The feature is not universal among ringforts, and its presence here suggests a site of some complexity. Killanin and Duignan noted the site in their 1967 survey of County Galway. A second ringfort lies approximately 170 metres to the northeast, a reminder that in early medieval Ireland these enclosures often appear in clusters, reflecting the dense, dispersed settlement patterns of the period rather than isolated individual farmsteads.