The enclosure measures approximately 36 metres east to west and 34 metres north to south, and its defining feature, an earthen bank, survives best along the south-western to north-western arc, where it rises to about a metre in height on the interior side. Elsewhere the bank is broken by numerous gaps, and nobody has yet been able to identify where its original entrance once stood.

This kind of earthen enclosure is broadly classed as a ringfort, the most common monument type in the Irish countryside, typically dating from the early medieval period, roughly the fifth to the twelfth centuries. Ringforts, known in Irish as raths or lios depending on regional tradition, served as enclosed farmsteads, their banks and ditches marking the boundary of a household rather than a military fortification in any serious sense. At Dunmadigan, the outer fosse, a ditch running around the outside of the bank, appears to have been re-cut at some point along its western and northern stretches, suggesting the site saw continued use or maintenance after its initial construction. The bank itself has been absorbed into a later field boundary, which is partly why it survives at all; generations of farmers found it easier to work with the existing earthwork than to remove it entirely.