These circular enclosures, typically formed by one or more earthen banks and ditches, were the farmsteads of early medieval Ireland, home to farming families of various social standings between roughly the fifth and twelfth centuries. They are so numerous across the Irish midlands that they can seem almost unremarkable, yet each one represents a particular household, a particular patch of ground, a particular moment in the slow organisation of early Irish society.

Westmeath is especially well furnished with such monuments, sitting as it does in the broad, glacially shaped lowlands of the Irish midlands, where good agricultural land encouraged dense early medieval settlement. A rath of this type would originally have enclosed a family's dwelling, outbuildings, and livestock within a raised earthen ring, the bank serving both as a boundary marker and as a modest form of defence. The townland name Ballynacroghy itself hints at older layers of local identity, townland names in Ireland frequently preserving traces of landscape features, family associations, or long-vanished land uses that written records never bothered to capture.