The one at Castlereagh in County Mayo is a case in point: a rath, which is the earthwork form of a ringfort, typically consisting of one or more circular banks and ditches enclosing a central area that would once have served as a farmstead or defended homestead during the early medieval period, roughly between the fifth and twelfth centuries. They were the everyday settlements of farming families, not the grand fortresses the name might suggest, and the sheer number of them that survive, often as low grassy banks in the corner of a field, speaks to how densely populated and agriculturally active early medieval Ireland was.

The Castlereagh example sits in a part of Mayo that carries considerable historical weight in its placename alone. Castlereagh, from the Irish Caisleán Riabhach, meaning the grey or brindled castle, suggests a later medieval presence in the area as well, pointing to layers of occupation that stretch across different periods. Raths like this one were typically built and occupied by free farming families of middling status, and many remained in use, or were at least remembered as significant enclosures, long after their original function had faded. Whether this particular earthwork survives intact, has been modified by later agricultural activity, or retains any visible surface features is not currently documented in available public records.