Those forces which were part of the monastic foundation at Cluny, established in 909 as a reform movement based on the Benedictine Rule. Although Cluny came to an end legally in 1790, after a long decline (despite reforms in the seventeenth century), it was the center of monastic reform and experiment for two centuries, having a vast network of communities (more than 1,100 at its height) attached to the central hierarchy. Their reforms extended to older monasteries, and their adaptability to numerous situations brought great success, extending also into political life, for Cluniacs were much involved over the investiture struggle. Many of its monks became popes, cardinals, and bishops, and among its notable abbots were Odo, Odilo, Hugh, and Peter the Venerable.

Combating ecclesiastical decadence and withstanding the empire were not its chief concerns. Even though it grew weak because of its vastness, its mission was admirably accomplished. Cluny renewed the ideals of its predecessors as Cîteaux (see Cistercians) was to do for Cluny (though without the same cultural achievement). The order had centers in Germany, Italy, Spain, and England, in addition to France. It emphasized biblical scholarship and liturgical renewal, and at its height manifested the fruits of simplicity.

See J. Wollasch et al., Neue Forschungen über Cluny und die Cluniacenser (ed. G. Tellenbach, 1959); and J. Evans, Monastic Life at Cluny, 910-1157 (1931).