Swedish nobility had no hereditary fiefs. In the case where a noble was granted a castle belonging to the crown, his heirs couldn't later claim their ancestors' civil or military rights. The lands of the magnates who constituted the medieval nobility were their own and not "on lease" from a feudal king. If they by their own means or exploitation of peasants built a castle and financed troops, then the castle was theirs, but the troops were expected to serve as a part of the army of the realm. In Sweden, there never existed serfdom. Hence, nobility was basically a class of well-off citizens, not owners of other human beings. In the Middle Ages and much of the modern age, nobles and other wealthy men were landowners, as well as lords of villeins and servants. Members of the nobility utilized their economic power and sometimes also other powers to have small-farm owners sell their lands to manor lords, so landowning centralized gradually more in the hands of the noble class.