What appears at first to be a natural undulation resolves itself into something deliberate: a near-perfect circle of earthworks, measuring roughly 60 metres north to south and 58 metres east to west, still largely intact after more than a thousand years of exposure to the Atlantic margins.

This is a rath, the most common type of early medieval settlement monument found across Ireland. A rath typically consists of one or more circular earthen banks enclosing a central living area, and was home to a farming family of middling status during the early medieval period, roughly 500 to 1100 AD. The Beagh example is well-preserved, retaining its substantial inner bank, an intervening fosse (a ditch cut to deepen the defensive profile of the bank above it), and an outer bank beyond that. The combination of bank, fosse, and second bank gave the enclosure both a practical barrier against livestock straying and a degree of social signalling; the effort involved in construction reflected the standing of whoever commissioned it. A well-defined entrance faces north-east, which may have been a deliberate orientation, though many raths simply took advantage of the most practical point of access on a given slope.