The site measures roughly forty metres across on its north-south axis, and what gives it a slightly unusual character is the entrance. On the south-west side, a causewayed gap four metres wide interrupts the banks and the intervening fosse, the fosse being the flat-bottomed ditch dug between the two rings of earthwork. Causeways like this are relatively common in Irish ringforts, but here it reads clearly in the ground, a deliberate threshold rather than a later breach.

Ringforts, known in Irish as raths when constructed from earth and stone, were the most common form of rural settlement in early medieval Ireland, typically dating from roughly the fifth to the twelfth century. They served as enclosed farmsteads, the banks providing security for livestock and household alike. At Rath Beg, the inner bank has suffered more than the outer, reduced in places to a scarp, a low sloped edge rather than a proper raised bank, with a modern gap three metres wide cut through the northern side. The outer bank has fared considerably better, and holds a notable quantity of stone within its width of three metres. This may not be original construction material so much as accumulated field clearance debris, stones gathered from surrounding land over generations and pushed up against a convenient existing boundary. There is no external fosse beyond the outer bank, which distinguishes the site slightly from more elaborate multivallate examples elsewhere in the midlands.