Merrion Castle  Merrion Castle was a castle situated in present-day Mount Merrion, to the south of Dublin city centre. Built in the early fourteenth century, it was from the sixteenth century to the early eighteenth century the principal seat of the Fitzwilliam family, who later acquired the title Viscount Fitzwilliam. After the Fitzwiliams moved to Mount Merrion House in about 1710 the castle fell into ruin, and it was demolished in 1780. No trace of Merrion Castle survives today. It was located opposite Merrion Gates, on the site of St. Mary's Home and School for the Blind. Its location, and the modern site of St.Mary's, can be seen on historical maps. The first mention of a castle at Merrion is in about 1334, when it was in the possession of Thomas Bagod, a descendant of Sir Robert Bagod, who had built Baggotrath Castle about 1280. In the late fourteenth century Merrion Castle was owned by Sir John Cruise, a leading diplomat and soldier. In the fifteenth century both castles came into the possession of the Fitzwilliam family, who became the most substantial landowners in Dublin; James Fitzwilliam, the Chief Baron of the Irish Exchequer, married Sir John Cruises's daughter. Until the late sixteenth century Baggotrath was the Fitzwilliams' favoured home, for possession of which they fought a bitter private war with the Cornwalsh family in the 1440s. It was Sir Thomas Fitzwiliam, grandfather of the first Viscount, who in the reign of Elizabeth I made Merrion Castle the principal family residence. During the English Civil War, possession of such a strong fortress so close to Dublin was clearly of crucial importance to both sides in the conflict. The Fitzwilliams, who were staunch Royalists, installed a strong garrison; but in June 1642 the castle was betrayed to the Parliamentary side, and remained in Parliament's hands until the Restoration. The second Viscount, Oliver Fitzwilliam, later Earl of Tyrconnell, who had some influence with Oliver Cromwell's son Henry Cromwell, pleaded for its return, but without success. Given the traditional loyalty of his family to the Stuart dynasty, he might well have expected its speedy recovery in 1660; but the bitter divisions in post-Restoration Ireland, which saw Tyrconnell accused by his enemies of being a supporter of Oliver Cromwell, caused a delay in the full restitution of his lands, and he did not recover Merrion until 1663.