Most ringforts in Ireland occupy elevated ground, their earthen banks commanding a view of the surrounding countryside. The one at Ballyhagan, in County Kildare, does the opposite. It sits on level, wet, rushy pasture, waterlogged enough that the interior is permanently rush-covered and the outer fosse, a shallow defensive ditch encircling the bank, fills with water rather than offering any obvious strategic advantage. That anomaly is part of what makes it worth a second look.

A ringfort, sometimes called a rath, is a roughly circular enclosure defined by one or more earthen banks and ditches, most commonly built during the early medieval period in Ireland as a farmstead or settlement. The example at Ballyhagan is poorly preserved but still legible in the landscape. The surviving bank measures around 53 metres in internal diameter and varies considerably in width, from under two metres on the southern side to more than four metres along the west. Its height, both internally and externally, is modest, no more than half a metre in most places, and along the eastern arc it has been reduced to little more than a low scarp in the ground. The outer fosse mirrors this unevenness, widening from roughly two metres in the south to five metres on the western side, and is now filled with rushes and standing water. A gap of about two metres at the north-west, heavily poached by cattle over the years, may represent the original entrance through which people and animals once passed. Despite the waterlogged setting, the overall shape and arrangement of bank, ditch, and probable entrance are consistent enough with known ringfort forms that the identification holds, even if the choice of location remains something of a puzzle.