What allowed cities to grow in the tenth and eleventh centuries?

Although historians disagree about the extent of the social and material damage caused by the 9th- and 10th-century invasions, they agree that demographic growth began during the 10th century and perhaps earlier. They have also identified signs of the reorganization of lordship and agricultural labour, a process in which members of an order of experienced and determined warriors concentrated control of land in their own hands and coerced a largely free peasantry into subjection. Thus did the idea of the three orders of society—those who fight, those who pray, and those who labour—come into use to describe the results of the ascendancy of the landholding aristocracy and its clerical partners. In cooperation with bishops and ecclesiastical establishments, particularly great monastic foundations such as Cluny (established 910), the nobility of the late 11th and 12th centuries reorganized the agrarian landscape and rural society of western Europe and made it the base of urbanization, which was also well under way in the 11th century.

monasticism. people often do monasticism in monasteries