One section has even been absorbed into a working field boundary, its military origins all but forgotten to the casual eye. Yet the dimensions tell a different story: a rectangular enclosure roughly 30 metres by 38 metres, defined by substantial ramparts and outer fosses, the ditches dug to reinforce and front the earthen walls.

The structure dates to 1689, when it was constructed by Colonel Wolseley, almost certainly in the context of the Williamite war then convulsing Ireland. A fort or earthwork of this kind, known as a fieldwork or sconce, was a practical defensive response to the era's military pressures rather than a permanent fortification in stone. Researchers Bradley and Dunne, writing for the Office of Public Works in 1989, proposed that the site was originally square in plan, with triangular platform bastions set into each of the four interior corners. Bastions of this type allowed defenders to cover the adjacent walls with flanking fire, a design principle that had become standard in European military engineering over the preceding century. What survives today is the western and south-western rampart in its most complete form, along with portions of the northern bank. A wide break of about four metres in the centre of the western rampart preserves what appears to be the original entrance, complete with an outer causeway, while a narrower gap of under a metre in the northern rampart may represent a secondary passage or a later breach.