That mound is almost certainly spoil from the construction of a nearby railway line, which means this early medieval enclosure has spent at least a century and a half carrying the debris of the industrial age on its back.

The site is a rath, the Irish term for a ringfort, the most common type of early medieval settlement monument in the country. Typically dating from roughly the sixth to the twelfth century, raths were enclosed farmsteads, their circular earthen banks and external ditches, known as fosses, defining the domestic space of a farming family rather than a military garrison. This example in Derradd is sub-circular, measuring approximately thirty metres north to south and twenty-eight metres east to west, with a bank around six metres wide and a slight fosse running alongside it. The entrance survives clearly at the north-east, where a gap of around four and a half metres wide opens onto a causeway nearly eight metres across. Bog lies close on two sides, forty-five metres to the north-east and one hundred and thirty metres to the south-west, which places this enclosed ground on a slight natural rise, evidently chosen to keep the interior as dry as the landscape would allow. It did not entirely succeed; the interior is marshy today and slopes gently from south to north, with faint traces of cultivation ridges running north-west to south-east, suggesting the ground inside the bank was at some point worked rather than simply occupied. A post-1700 field boundary cuts across the site from north-west to south-west, adding another layer of agricultural history over the early medieval one. The railway that deposited the spoil mound passes close by, with Inny Junction just two hundred metres to the north-west, so this small enclosure has ended up wedged between the rhythms of the early medieval countryside and the engineering of the nineteenth century.