What makes the site particularly striking is the layering of occupation it implies. The enclosure did not simply fall out of use; it was built over, its boundaries interrupted by the construction of a rath, a type of circular earthwork farmstead common in early medieval Ireland, which cut directly into the older structure and left only a portion of the original ditch accessible to later investigation.

The enclosure measured roughly 37.5 metres by 31 metres and was defined by a fosse, essentially a ditch dug to mark or defend a boundary. It came to light during pre-development archaeological testing ahead of the Herons Wood housing development at Carrigaline Middle, with work carried out and reported by Sherlock in 2002 and 2004. Only the western arc of the fosse survived outside the footprint of the rath, and it was this stretch, around 30 metres in length, that could be properly excavated. The ditch itself was modest but carefully shaped: 1.6 metres wide and 0.9 metres deep, with sides that sloped evenly down to a flat base between 0.3 and 0.4 metres across. It had filled over time with a stony silty clay. No features of archaeological significance were found in the western portion of the interior that was opened up, which suggests either that activity was concentrated elsewhere within the enclosure, or that whatever once stood there left no lasting trace in the ground.