Where the land narrows and the sea drops away on multiple sides, early builders would cut a ditch or raise an earthen bank across the neck of the promontory, effectively turning a peninsula or island spur into a fortified enclosure with minimal effort and maximum natural protection. Hundreds of such sites are known around the Irish coastline, and they date broadly from the Iron Age, though many were likely used and reused across long periods. The one on Rabbit Island belongs to this widespread but quietly compelling tradition of coastal defence.