This is a rath, the Irish term for a ringfort, a type of enclosed settlement built in great numbers across Ireland during the early medieval period, roughly between the fifth and twelfth centuries. Farmers and minor lords constructed them as farmsteads, surrounding a circular living area with earthen banks and ditches to protect people, livestock, and stored goods. The one at Ballyspellan sits at the western end of a slight east-west ridge, positioned just high enough above the valley floor to command clear views in every direction, which was almost certainly the point.

The enclosed area measures thirty metres in internal diameter, ringed by a bank roughly two metres wide, rising one metre on the interior side and between two and a half and four metres on the exterior, a difference that reflects how the spoil from the outer ditch, known as a fosse, was piled inward to heighten the defensive effect. That fosse reaches a maximum width of six metres in the northern and eastern quadrants, where the earthworks survive in their best condition. Elsewhere the monument has suffered considerable degradation over the centuries, reduced by agricultural activity and the gradual levelling that comes with ploughing and grazing. What makes the site particularly interesting is evidence in the north-western sector of outer banks with their own external fosses extending as much as thirty metres beyond the main upstanding structure. These traces of a more elaborate, multi-vallate enclosure, one with multiple concentric rings of banks and ditches, hint that this was once a more substantial and possibly higher-status site than its present worn condition suggests.