The raised interior platform measures roughly 43 metres across, and what surrounds it is not a single simple bank but a layered defensive arrangement: an inner bank of earth and stone, a fosse (a ditch cut into the ground, designed to slow or stop approach), and then an outer bank beyond that. The fosse alone runs to about five metres wide and drops one and a half metres deep, which in practical terms is a serious obstacle. Whatever this structure was built to protect or announce, its builders were not working casually.

The earthwork belongs to a class of site broadly described as a ringfort, a form of enclosed settlement common across Ireland from the early medieval period onwards, though many such sites have origins or phases of use that are difficult to pin down without excavation. At Lisraherty, the defences are not uniform around the perimeter. From the south-east, south, and north, the inner bank is the dominant feature; elsewhere, a scarp of two to three metres takes over that role. The outer bank, which runs from the north-north-east around through the east to the south, has been altered over time and absorbed into a field boundary, which explains why the site reads differently from different angles. A report from 1990 proposed that a gap in the inner bank at the south-east, accompanied by a causeway crossing the fosse, represents the original entrance point, meaning the approach would have required crossing that ditch by a controlled and deliberate route rather than simply walking up to it.