Subinfeudation is the term for the hierarchical structure that existed between Lords and their Vassals in the middle ages. At the top of the structure there were kings. The kings in turn had Vassals who were powerful Lords or Barons. These powerful Lords were also major land owners, who in turn had Vassals who may have been lesser land owners, but still powerful, each Lord in turn has it's own Vassals terminating with the lowest level subordinate knights or minor land owners. This hierarchy was not a formal system of government, but the natural extension of feudal practice in the middle ages.