Local tradition holds that this fortification was built during the reign of Elizabeth I, sometime in the late 16th century, only to meet its demise around 1650 at the hands of Oliver Cromwell’s forces during their campaign through Ireland. The Down Survey maps from 1655-6, commissioned by Cromwell’s government to document confiscated lands, mark the location with a cluster of cabins and describe it as a ‘decayed old castle’, which by 1640 had belonged to John Power of nearby Dunhill.

Today, nothing of the castle remains visible above ground, though its presence lingers in the historical record and local memory. Archaeological testing carried out in 2002 approximately 30 metres southwest of the site yielded no materials directly related to the castle itself, but did uncover two quernstones; grinding stones used for milling grain; during the dismantling of an existing building. These artefacts hint at the everyday agricultural life that would have sustained the castle’s inhabitants and the surrounding community.

The castle’s destruction fits a familiar pattern across Ireland, where Cromwell’s military campaign systematically targeted fortifications held by Catholic landowners and those loyal to the Royalist cause. The fact that it appears as already ‘decayed’ in records from just a few years after its supposed destruction suggests either a particularly thorough demolition or that the castle had already fallen into disrepair before Cromwell’s arrival. The Power family who owned it were prominent landowners in the area, and Dunhill, their main seat, still contains visible castle ruins today, making this lost fortress at Castlereagh a lesser satellite of their holdings in medieval and early modern Waterford.