In the later 9th century and all through the 10th century, the West experienced one of the darkest periods in its history. New waves of invasions, especially by Vikings and Muslim Arabs, destroyed the relative security of the empire created by Charlemagne. The Church suffered from the domination of lay lords. Communication with the East was virtually cut off, partly because of the Arabs’ power in the Mediterranean emanating from their strongholds in Crete and Sicily. In 996 the first German was elected as pope of Rome, with the name Gregory V.
In 910 the Monastery of Cluny was founded in Burgundy in eastern France, by William the Pious, Duke of Aquitaine. Under its first abbot, Berno of Baume (d. 927), high standards of monastic observance were set and followed—including a return to the strict Benedictine Rule first established by Saint Benedict of Nursia in the 6th century, independence from lay control, and economic self-sufficiency. By the time of Berno’s death, several neighboring monasteries had adopted Cluny’s standards, and under Berno’s gifted successors, especially Saint Odo (r. 927–942) and Saint Odilo (r. 998–1048), hundreds of monasteries, especially in France and Italy, adopted these reforms. These “Cluniac houses” became a major force for general reform in the entire Western Church in the 11th century.