These structures, known in Irish archaeology as dúnta, typically date from the Iron Age or early medieval period and work with the landscape rather than against it: a narrow neck of headland is cut off from the mainland by one or more earthen or stone ramparts, while the sea does the defensive work on the remaining sides. The result is a naturally fortified enclosure that required far less labour than an inland ringfort of equivalent size, and far more nerve to occupy in a winter storm.

Gleann Lára sits on the north Mayo coast, a stretch of shoreline that saw continuous human activity from the Neolithic period onwards, much of it now only legible as earthworks and eroded field systems. Promontory forts in this part of Connacht are not uncommon, but each occupies its own particular configuration of rock and sea, and the one at Gleann Lára remains poorly documented in the published record. What can be said with confidence is that whoever chose this headland understood both the tactical logic of sea cliffs and the symbolic weight of an elevated coastal position, visible from the water and commanding views along the shore.