The medieval era of European history (also known as the Middle Ages), lasting from approximately 900 to 1400 A.D., is notable as the transitional period between the Dark Ages and the rebirth of Greco-Roman thought known as the Renaissance. Characterized by frequent hardships, such as the grain famines of the 1300s and the bubonic plague, medieval society was politically defined by fuedalism, a system of government by which a monarch controls a hierarchy of lesser vassal lords through oaths of allegiance. Economically, medieval Europe was driven by the manorial system, which legally bound peasants to their lord's land. The medieval era generally witnessed a weakening of the social fabric and networks of learning put in place by Roman rule; European society did not regain the level of sophistication it possessed under the Caesars until the 1400s.