Founded in 910 to return to the authentic monasticism of Saint Benedict, the abbey of Cluny led a revolution in the medieval Church. Wresting secular hands from control of monastic offices and finances, the great Burgundian monastery and its hundreds of daughter houses inspired eleventh-century churchmen to seize control of the Church from petty lords and outraged emperors. Powerful and respected, the Cluniac Order cast a long shadow over the European Church, but its very position of leadership brought prosperity into the cloister and, in its train, complacency. The Cistercians were founded...