Rosslare Fort once occupied the northern tip of a sand-spit roughly five and a half kilometres long, forming the eastern edge of Wexford Harbour. The narrow neck of that spit was breached in two places in 1924, and the community living there had no choice but to leave. By January 1925, the place was empty. The walls visible above the water today are the last traces of a site that appeared on maps as far back as 1599.

The fort itself had a long and contested history before the sea made the question of ownership irrelevant. It appears on Boazio's map of 1599 and again on Speed's map of 1610, and by 1642 the Confederate Catholics, a governing alliance of Irish Catholic clergy and nobility formed during the wars of that period, had refortified it with seven guns. The garrison surrendered to Cromwellian troops advancing along the sand-bar from the south on 10 October 1649. A survey map produced during the Cromwellian Down Survey of 1655 to 1656 shows it as a rectangular feature with a single projecting bastion at the eastern angle. After that, the fort transitioned into something more administrative than military: a station for Revenue officers and harbour pilots, alongside a fishing settlement. Around 1800, a Catholic chapel was quietly opened in an upstairs room at the southern angle of the Square, an open cobbled area at the northern end of the village that likely represents the original core of the fort. About ten pilots lived communally to the south of the Square, and a wooden lighthouse stood at the point, with a flagstaff carrying suspended balls to signal tidal conditions to incoming vessels. The fort was not entirely done with conflict, though. In 1798, two hundred rebels held it with three pieces of artillery before being forced out by a naval force under Captain Thomas Williams on 21 June. A martello tower, the squat, thick-walled coastal defence structures built across Ireland and Britain during the Napoleonic period, was added in 1805 to 1806 at a cost of £2,300, positioned to give Revenue officers and pilots a longer view of ships approaching the harbour.

The Revenue officers withdrew in the 1850s, the chapel closed not long after, and the school shut in 1882. A lifeboat station operated at the fort at various points between 1838 and 1924, the last connection to organised maritime life before the land itself gave way. The site is now inaccessible, the three-kilometre stretch of narrow sand-bar that once formed the approach having been washed away entirely.