The enclosure is subcircular in plan, measuring roughly 28.5 metres on its longer axis and 25 metres across, and is defined by an earthen bank reinforced by a hedge. What gives it particular character is the outer fosse, a defensive ditch running along the eastern to southern arc, its base still some 4.5 metres wide. A ramp entrance at the south-southwest, about 2 metres wide at its base, marks the original point of passage into the interior.

This kind of earthwork is generally understood to be a rath, sometimes called a ringfort, the most common field monument in Ireland. Raths were typically enclosed farmsteads built during the early medieval period, roughly between the fifth and twelfth centuries, though many were in use for generations before and after that broad span. The enclosing bank and fosse served both as a practical boundary for livestock and as a marker of status and territory. The fosse at Lisoarty, present only along the eastern and southern sides, suggests either that the natural topography of the hill provided sufficient definition on the other sides, or that construction was adapted to the local lie of the land. The interior height of the bank is relatively modest at around half a metre, while the exterior face rises to about 1.5 metres, a modest but deliberate defensive profile that would have made casual entry uninviting.