The Castle was used as a centre of Norman administration for the Liberty of Meath, one of the new administrative areas of Ireland created by Henry II of England and granted to Hugh de Lacy. de Lacy took possession of it in 1172. De Lacy built a huge ringwork castle defended by a stout double palisade and external ditch on top of the hill. There may also have been further defences around the cliffs fringing the high ground. Part of a stone footed timber gatehouse lies beneath the present stone gate at the west side of the castle. The ringwork was attacked and burnt by the Irish but De Lacy immediately rebuilt it in 1173. His son Walter continued rebuilding and the castle was completed c 1204. The next phase of the castle’s construction took place at the end of the 13th century, and the beginning of the 14th century. A new Great Hall with undercroft beneath it and an with attached solar in a radically altered curtain tower, and a new forework forebuilding, and stables were added to the keep. After de genneville's death his widow Joan married Roger Mortimer and the castle passed to the Mortimer family who held it until the lord of Trim became Edward IV king of England in 1461.
During the late Middle Ages, Trim Castle was the centre of administration for Meath and marked the outer northern boundary of The Pale. In the 16th and 17th centuries it had declined in importance, except as a potentially important military site, and the castle was allowed to deteriorate. During the 15th century the Irish Parliament met in Trim Castle seven times and a mint operated in the castle. It fell into decline in the 16th century but was refortified during the Cromwellian wars in the 1640s.
After the wars of the 1680s, the castle was granted to the Wellesle family who held it until Arthur Wellesley (the Duke of Wellington), sold it to the Leslies. In following years it passed via the Encumbered Estates Court into the hands of the Dunsany Plunketts. They left the lands open and from time to time allowed various uses, with part of the Castle Field rented by the Town Council as a municipal dump for some years, and a small meeting hall for the Royal British Legion erected. The Dunsanys held the Castle and surrounds until 1993, when after years of discussion, Lord Dunsany sold the land and buildings to the State, retaining only river access and fishing rights.
The Office of Public Works began a major programme of conservation and exploratory works, costing over six million euro, including partial restoration of the moat and the installation of a protective roof. The castle was re-opened to the public in 2000.
Structure
The central three-story building, called a keep, donjon or great tower, is unique in its design, being of cruciform shape, with twenty corners. It was built in at least three stages, initially by Hugh de Lacy (c.1174) and then in 1196 and 1206 by Walter de Lacy. The keep was built on the site of a large ring work fortification that was burnt down in 1172 and rebuilt in 1173, following attacks by the Gaelic King of Connacht, Ruaidrí Ua Conchobair Rory O'Connor.
The surviving curtain walls are predominantly of three phases. The west and north sides of the enciente are defended by rectangular towers (including the Trim Gate) dating to the 1170s, the Dublin gate was erected in the 1190s and the remaining wall at the south wih its round towers dates to the first decade of the 13th century. There were two main gates into the castle. That at the west side dates to the 1170s and sits on top of s a demolished wooden gateway. The upper stories of the stone tower were altered to a semi octagonal shape c. 1200AD. A single round towered gate with an external barbican tower lies in the south wall and is known as the Dublin Gate. It dates from the 1190s.
Apart from the keep the main structures surviving in the castle consist of the following: an early 14th century three towered fore work defending the keep entrance and including stables within it and which was accessed by a stone causeway crossing the partly in filled ditch of the earlier ringwork; a huge early fourteenth century three aisled great hall with an under croft beneath its east end opening via a water gate to the river; a stout defensive tower turned into a solar in the early fourteenth century at the northern angle of the castle; a smaller aisled hall added to the east end of the great hall in the fourteenth or fifteenth century; a building (possibly the mint) added to the east end of the latter hall; two fifteenth or sixteenth century stone buildings added inside the town gatehouse, 17th century buildings added to the end of the hall range and to the north side of the keep and a series of lime kilns, one dating from the late 12th century the remainder from the eighteenth and nineteenth centuries.
