This could be the site of Inis-Ochta castle, where historical records tell us Melaghlin Mac Rannall was held prisoner by Con O’Rourke in 1499, according to the Annals of the Four Masters. The island, known as Port Island near Port, County Cavan, offers a glimpse into the turbulent medieval history of the region.

Archaeological surveys conducted by Davies in 1947 documented the foundations of a circular tower on the island, with an internal diameter of 6.8 metres. The structure’s walls, built from dressed stone and mortar, measure 1.37 metres thick and survive to a height of 1.8 metres, featuring a distinctive sloping outer face known as a batter. The tower contains three deep recesses with loopholes for defence, and Davies suggested the entrance was likely positioned on the first floor; a common defensive feature in medieval Irish tower houses. Several small rectangular stone structures of unknown age dot the island, including one on the western side of the tower that appears to have been built separately rather than integrated into the main structure.

Today, the island has become completely overgrown with dense vegetation, making archaeological inspection impossible without significant clearance work. The site remains unvisited by recent surveys, with the most recent documentation dating from the Archaeological Inventory of County Cavan published in 1995, though some details were updated in 2008. This remote and forgotten fortress stands as a tantalising reminder of the O’Rourke clan’s power in medieval Breifne and the strategic importance of controlling the waterways between modern Cavan and Fermanagh.