This fortification, built on a natural headland jutting into the sea, represents a type of defensive structure particularly common along Ireland's Atlantic coast. These forts typically date from the Iron Age through to the early medieval period, when communities needed both the strategic advantage of height and the natural protection offered by steep cliffs and crashing waves below.

Promontory forts like Lurganboy served multiple purposes; they were defensive strongholds, centres of trade, and symbols of power for local chiefs. The Greenfort name hints at the earthen banks that likely still define its boundaries, now covered in grass and merged seamlessly with the landscape.