A rath, to use the Irish term, is a roughly circular enclosure built during the early medieval period, typically between the fifth and twelfth centuries, and used as a farmstead or high-status residence. This one at Garrane measures 46 metres across in both directions, making it a reasonably substantial example, and it retains enough of its original structure to reward a careful look.

The enclosing earthen bank stands to a height of around 1.1 metres along its eastern to west-northwest arc, while elsewhere the boundary takes the form of a scarp, a cut or shaped slope in the ground, rising to approximately 1.3 metres. In several places both the bank and the scarp are stone-faced, suggesting either that the original builders reinforced the earthwork with drystone walling, or that later occupants did so. An external fosse, the technical term for a surrounding ditch, runs along the north-northeast to eastern side, reaching a depth of up to 0.8 metres. This combination of bank, scarp, and ditch would have presented a layered boundary to the outside world, less a fortress wall than a clear statement of enclosure and ownership. Most interesting, perhaps, is the original entrance: a gap of 1.5 metres in the eastern bank, still accompanied by a causeway that once allowed people and animals to cross the fosse and pass inside.