The example at Castlecarra in County Mayo takes a different approach entirely. It is an inland promontory fort, a type that uses the jutting tongue of a raised landform, a river bend, a bog margin, or a similarly awkward piece of terrain to achieve the same effect far from any coastline. The basic principle is the same as its coastal cousins: nature provides two or three sides of the enclosure, and the builders need only close off the exposed neck with a bank or a ditch. The result is a fortified position that is considerably harder to approach than its modest earthworks alone would suggest.

Inland promontory forts are less numerous than their coastal equivalents and tend to attract less attention, which makes each surviving example worth noting. The Castlecarra site sits in an area of County Mayo with a long history of early settlement, in the broad lowland landscape around Lough Carra, a shallow, limestone-filtered lake whose clear waters have drawn people to its margins since prehistory. The specific details of who built this particular fort, and when, remain unrecorded in the sources currently available, but the fort type in general belongs to the Iron Age and early medieval periods in Ireland, when controlling a commanding piece of ground had obvious practical value for a local dynasty or farming community that needed somewhere defensible to retreat to or to hold.