It is a rath, the Irish term for an earthen ringfort, a type of enclosed farmstead built and occupied predominantly during the early medieval period, roughly between the fifth and twelfth centuries. Thousands of them survive across Ireland, yet each one sits differently in its landscape, and this one, measuring roughly 25 metres east to west, occupies a gently angled hillside that would once have given its inhabitants a clear view southward.

The enclosure follows a design that was well established across early medieval Ireland. An inner earthen bank rises about one metre above the interior and 1.2 metres above the surrounding ground, with a fosse, that is a ditch, cut between the main bank and a secondary outer bank. Here the fosse is V-shaped in profile and remains damp in places, suggesting the underlying ground retains water. The outer bank, standing at around 0.6 metres, survives from the west-south-west around to the east. Entry was made through a causewayed gap to the south-south-east, nearly four metres wide, where the ditch was bridged to allow passage. A cattle gap has been cut into the northern side at some point, reflecting the fort's later life as an ordinary field boundary rather than a defined enclosure. The interior is now overgrown with scrub.

The causewayed entrance facing roughly south is a detail worth pausing over. Many ringforts across Ireland share this southward orientation for their entrances, possibly for practical reasons to do with light and prevailing wind, though the pattern is not universal. Here, combined with the south-facing slope, it suggests a settlement that was deliberately positioned to make the most of its aspect on Boy Hill.