At Cashel in County Carlow, what remains of a rath, the Irish term for a roughly circular earthen enclosure used as a farmstead during the early medieval period, amounts to little more than a ghost in the ground: a circular area some 31 metres in diameter, bounded by a bank that now rises only about ten centimetres above the surrounding surface. Tens of thousands of ringforts were built across Ireland between roughly the fifth and twelfth centuries, and a great many have been reduced by centuries of ploughing and field clearance to exactly this kind of near-invisible trace.