The castle occupies a strategic position with commanding views to the north and east, sitting just 700 metres from the Meath border in the parish of Killucan. Built sometime in the 14th or 15th century, the structure underwent significant modifications in the 16th century when it was extended to the southeast, transforming it from a simple square tower measuring 9.9 metres per side into a more complex fortification with additional mural chambers and a new entrance. The D’Arcy connection dates back to 1336 when John D’Arcy, 1st Baron D’Arcy de Knayth, received the manor of Rathwire from Edward III; the lands of Rattin likely formed part of this grant.

By 1600, the castle belonged to Thomas Darcy Fitz Walter, with various branches of the family maintaining residences throughout the region, including Hyde Park House in Killucan. The castle’s fortunes declined during the turbulent late 17th century when Nicholas D’Arcy of Platten, who held Rattin, sided with the Jacobites and was subsequently attainted in 1691. Following his forfeiture, the estate, comprising 701 statute acres, was sold by the Commissioners of Forfeited Estates to Ephraim Dawson of Dublin in 1703 for £3,490. A 1902 drawing by Reverend William Falkiner shows the castle still possessed an impressive 17th century chimneystack rising from its southwest wall, though this feature collapsed sometime after 1942, taking the north corner of the structure with it.

Today, the castle remains an imposing ruin, standing four storeys high with walls constructed of random rubble masonry. The original northwest section features rounded corners typical of earlier Irish tower houses, whilst the later southeast extension displays square corners with a pronounced base batter. Inside, visitors can still observe fascinating architectural details including wicker centring marks on the vaulted ceilings, a murder hole above the entrance lobby, and a stone vaulted guard chamber complete with wall niches. The thick walls, measuring up to 2.2 metres in places, are honeycombed with mural chambers, stairs and passages, particularly on the eastern side where several substantial vaulted rooms survive, testament to the castle’s former grandeur and defensive capabilities.