The major economic system of feudalism was primarily based upon land ownership and the exchange of services for protection. In this medieval system, land, or fiefs, was held by nobles or lords, who granted portions of it to vassals or knights in exchange for military service. At the bottom of this hierarchy were serfs and peasants, who worked the land and provided agricultural produce in return for protection and various obligations to their lords. This decentralized system was characterized by a rigid social structure and mutual obligations and dominated much of medieval European life.