These structures, known in Irish as raths, were the standard farmsteads of early medieval Ireland, typically consisting of a raised circular area enclosed by one or more earthen banks and ditches. They were domestic spaces, not military fortifications, and tens of thousands of them survive across the island in varying states of preservation. The one at Crillaun is among the less-documented examples.

Ringforts were built predominantly between around 500 and 1000 AD, though some are older and some continued in use later. A typical rath would have sheltered a farming family, their livestock, and their outbuildings within the enclosure, the bank providing a boundary as much social as physical. In the west of Ireland, where stone was plentiful, these enclosures were sometimes built in drystone rather than earthwork, in which case they are called cashels or cahers. The Mayo landscape is scattered with both types, many still visible as cropmarks, earthworks, or low grassed-over banks in fields that have been farmed continuously since long before anyone thought to record them.

The specific details of the Crillaun example, its dimensions, condition, whether it survives as a full circuit or only as a partial remnant, are not currently available in the public record. What can be said is that its presence in the townland places it within a pattern common to the whole of the west, where early medieval settlement left marks on the ground that outlasted the people who made them by more than a thousand years.