The enclosure measures around 28 metres across at its widest, defined by a bank of earth and stone that still rises nearly a metre on its interior face and slightly more on the outside. A shallow fosse, or external ditch, once reinforced the whole arrangement, though it has largely silted to little more than a gentle depression. Gaps have worn through the bank at three points, to the north-east, south-south-east, and south-south-west, almost certainly the result of centuries of livestock passing through rather than any deliberate breach.

This is a rath, the most common type of early medieval settlement monument in Ireland. Raths were typically enclosed farmsteads, their earthen banks and ditches serving as boundaries and as modest protection for a household and its animals rather than as serious fortifications. What makes the Tinnascart example particularly interesting is the detail that survives alongside the main enclosure. Adjoining the south-east bank on the outside is a small hut site, just over three metres long and under two metres wide, enclosed by its own low curving earthen bank and open to the south-west. Structures of this kind, positioned just outside or against the main bank, are thought to have served ancillary functions, perhaps as byres or storage spaces. More intriguing still is the possible souterrain recorded within the interior. Souterrains are underground stone-lined passages or chambers associated with early medieval settlements, their precise function debated but generally understood as places of refuge or cool storage. The bank itself has spread considerably over time due to slippage, which has softened and widened its profile and made it harder to read at first glance as an engineered structure.