A mediaeval form of social economic and political organization. Feudalism had a pyramidal structure. At its head was the king; below the king was a hierarchical chain of nobles, down to the lords of individual manors-the manor being the basic social and economic unit. The lords leased land to tenants, offering them protection in exchange for military and other services. Society was thus knit together in a network of obligation and service. The lowest part of the pyramid was occupied by serfs, who were obliged to cultivate the land belonging to their lord. There was thus no mobile middle class in feudalism; social rank was fixed by inheritance and could not be changed. When at the end of the Middle Ages a middle class did begin to emerge, it marked the beginning of the end of feudalism.