The Cistercian Abbey of Monasteranenagh (Manister), County Limerick, Ireland, was founded in 1148 by Turlough O’Brien, King of Thomond. Donal Mor O’Brien became patron of the abbey after Turlogh’s death. It was a daughter house of Mellifont and subsequently established three daughter houses (Abbeydorney, Midleton and Holycross). Its name derived from ‘Manister an Aonaigh’, the monastery of the fair, after a fair that was held at the site in ancient times. Its Latin name represents the latinisation of the local river: ‘Magium’, from the river Mague. The Abbey complex was built a little way from the river, on a section of slightly raised ground, which avoid flooding - the site is very flat.

The abbey was heavily involved in the ‘conspiracy of Mellifont’ and in 1227 affiliation of the abbey was transferred to Margam in Wales. In the following year the Irish monks forced the abbot and the non-Irish monks, who were mainly of Norman descent, to leave the abbey. The remaining monks attempted to prevent Stephen of Lexington from visiting the abbey by fortifying the precinct; they prepared the abbey for siege, turning it into a castle and building a tower above the altar. The ring leader was the King of Thomond, who resented the presence of the Anglo-Normans in Ireland. The community was excommunicated for revolting against their ecclesiastical superiors. Herbert de Burgo, the bishop of Limerick, eventually recaptured the abbey and reinstalled the monks who had been driven out; the rebellious monks returned and asked for mercy which was granted. By the end of the 13th century the abbey was in debt for £209, a fortune, to an Italian wool merchant, Ricardi de Lucca.

The abbey was suppressed in 1539-40, and the property was granted to Sir Osborne Echingham in 1543. However, the monks were left in possession of the abbey (it was outside of Anglo control which had shrunk to within the 'Pale') which they retained until 1580. Some of the monks who were expelled from affiliated abbeys in 1540-2 are said to have joined the community at Monasteranenagh. It was the scene of a major battle during the Geraldine rebellion of 1579-1580 and in 1579 Sir William Malby led the English into battle against the Irish and the Spanish. The Irish army, led by Sir John of Desmond, was defeated and the Spanish and Irish troops took refuge in the abbey. The English army turned its guns on the abbey and captured it; the abbot was reputed to have been beheaded on the altar steps and that forty monks were slain within the precinct. The abbey was burned  and the Cistercian community at Monasteranenagh ended. The buildings were further damaged in 1585 when it became the property of Sir Henry Wallop who plundered the abbey of all its valuables and left the ruins to decay.

Today, the ruins mainly include the church, which dates from 1170 to 1220, and an early Gothic chapter house. The walls, gables and the main window frame of the church are all extant. The tower fell in 1806-7; it was thought to have been either the crossing tower of the church or part of a 16th century house that was constructed over the south transept. The transepts held three chapels each which had groin or ribbed vaults and the presbytery had a barrel vault (which collapsed in 1874) and a crossing tower was added at some stage and later the complexes overall design was reduced in size. The interior of the abbey was used as a burial ground until the 1970s. A short distance from the abbey is another set of ruins which appears to be the remains of the old guesthouse. The ruins are situated on a flat plain, ten miles south of Limerick, and can be accessed by the public at all times (except when the fields are full of cattle).

Plan of the Abbey (Westropp, 1889):