The castle belonged to Arnold Fitz Eustace le Poer by 1317, placing it firmly within the Anglo-Norman sphere of influence during a turbulent period of Irish history. In 1448, it withstood an attack by Cathal O’Connor Faly, one of the Gaelic lords who frequently clashed with the English settlers in the Pale, but its luck ran out during the Confederate Wars when it was burnt in 1647 and later recaptured and destroyed by Colonel Hewson’s Cromwellian forces.

Today, what survives of this once-formidable stronghold is incorporated into the basement of an early 18th-century house, offering a fascinating glimpse into medieval defensive architecture. The rectangular structure, measuring 10.7 metres long and 5.2 metres wide internally, is built from uncoursed limestone rubble typical of medieval Irish construction. The original doorway appears to have survived, along with at least two blocked arrow loops featuring deep splays that would have allowed defenders to shoot at attackers whilst remaining protected. A later partition wall divides the space, but the barrel vaulted ceiling still bears traces of the original wicker centring used during its construction; a remarkable survival of medieval building techniques.

The castle’s position near a medieval church, which stands about 275 metres to the northeast, suggests this was once an important local centre of both secular and religious power. The proximity to the River Liffey would have provided both strategic advantages and practical benefits for water supply and transport, making Castlemartin a valuable property worth defending, and ultimately, worth destroying during Ireland’s bloody 17th-century conflicts.