The monks being vegetarian required an amount of arable land adjacent to a monastery as well as the facility to be able to channel running water to the establishment.

The Cistercians were welcomed and over many years were given land grants of about 50,000 acres (200 km2) scattered west of the River Shannon in 27 out-farms called granges.

This was due in part to the events of 1202 when during a war initiated over the succession to the kingship of Connaught, the abbey was occupied and very badly damaged.

The history continued to be full of incident, in the 1220s Boyle became involved in what was termed ‘The Conspiracy of Mellifont’ when that abbey and its various daughter houses attempted to break away from Norman control.

The last abbot Gelasius Ó Cuileanáin was executed in Dublin in 1580. The monastery was laid out according to the usual Cistercian plan, a church on the north side of a roughly rectangular cloister, with a chapter house for meetings of the monks on the second side, a kitchen and a refectory on the third, and probably storehouses and dormitory above on the fourth.

The church adheres to the Cistercian canon in having a nave with side aisles, a transept to the north and south of the crossing, each with a pair of chapels in the east wall, and a chancel, whose original windows were replaced in the thirteenth century.

The design was influenced by styles from Burgundy, from whence the Cistercians came to Ireland, but much of the detailing of the nave and particularly the cylindrical piers of the south arcade has strong echoes of the West of England.

A small piece of stone from the Abbey was carried to the other side of the world and placed on the monumental headstone of an Irishman Bartholomew Higgins in the Rookwood Necropolis in Sydney, Australia.