The original entrance, the point through which people and livestock once passed in and out of an enclosed early medieval farmstead, is gone entirely, leaving the earthwork as a kind of sealed oval, its domestic history locked inside.

A rath is a ringfort, the most common archaeological monument type in Ireland, typically consisting of a raised circular or oval area enclosed by one or more earthen banks and external ditches. This example at Ballybeg measures roughly 43 metres north to south and 38 metres east to west, defined by a scarp between 1.8 and 2.4 metres high. What distinguishes it somewhat from the general run of such sites is the fosse, the external ditch, which is partially rock-cut, meaning the builders had to work through bedrock to achieve the depth they wanted. At nearly three metres wide and one metre deep, it would have been a meaningful obstacle. That fosse survives, though only along the arc running from the south-west around through north to north-north-east; the rest has either silted up or been obscured by centuries of agricultural activity in the surrounding fields.