The feudal system of medieval Europe was based on mutual obligations, or personal bonds, between the king and his vassals rather than having been based on social or political relationships. The system was hierarchical and extended downward through bonds of personal loyalty between varying ranks of lordship and vassalage. The obligation of loyalty to the higher-ranking individual very often resulted in the vassal receiving a reciprocal allocation of land.
In exchange for land, the grant of which was known as a fiefdom, the vassal usually provided military protection or service to the higher-ranking lord. In certain cases, the obligation may have been based solely on a sworn oath of loyalty called a fidelitas. The act of swearing allegiance to a lord or king was often performed with a great deal of ceremony, and may have also included holy sacraments or the relics of saints. In times of war, however, the ceremony may have been dispensed with in order to hasten the process of enlisting the aid of vassal knights to pursue a military campaign.
When a vassal was provided land in exchange for loyalty, the peasants living on that land went along with it. In this way, the vassal was also given legal authority over those people living on the land. These peasants, or serfs, were required to work the land for no pay. The serf was neither a slave nor property, but was considered to be a fixture of the land. Serfdom was hereditary, and a serf's children were also tied to the land. At the lowest rung of the hierarchical feudal system, the serfs' obligation to their lord and landowner was to provide labor.