The abbey, built in the IX century, was founded by the Benedictines and is one of the best examples of Gothic-Cistercian architecture and is also the first building in Italy in this style.
In 1134 Pope Innocence II granted the abbey to the Cistercian monks who can take the credit for having built the church attached to the monastery.
The inside of the building is characterised by a stern monastic rigour, not leaving much room for decorations and frescoes.
The abbey has a cross layout, with three naves divided by 14 pillars that develop into bays with groin vaults.
The abbey complex includes: a rectangular cloister, in Gothic style along three sides and in Romanesque style along the fourth; a chapter-house dominated by dormitories; a refectory inside of which the reading pulpit is kept.
The guest lodgings are found in a separate building, the very same ones where Saint Thomas Aquinas lived out his last days.