The Benedictine abbey of Cluny was the cradle of a reform which drastically changed the western monastic tradition. Founded in 910, this abbey answered directly to Rome and was under the authority of a line of exceptional abbots. At its height of its influence in the 12th century, it was at the head of an "empire" that counted 10,000 monks. It was at this time, around 1088, that construction began on the third abbey church (Cluny III). Abbot Hugues de Semur (1049-1109) decided to build a huge church, 187 metres long, which remained the longest church in Christendom until the construction of Saint Peter's in Rome. Cluny became a national property during the French Revolution. Used as a stone quarry, it was systematically dismantled until 1823. It remains a part of the south arm of the transept. The 18th century convent buildings were spared destruction as were two abbot's residences dating from the 15th century, that of Jean de Bourbon and that of Jacques d'Amboise. In the first building, the Ochier Museum presents a collection of remains and models of the former monastery and the medieval village. In the flour mill, there are marble columns form the sanctuary of the abbey church and their capitals, which are masterpieces of Romanesque sculpture. Included in the tour : a 3D film gives a sense of the majesty of what was once Christendom's largest church.