The castle was the perfect defense system for its time. Many designs for safety and strength were fitted to the large structures such as walltops allowing maximum arrow range and minimal exposure to the fire of an attacking batallion. A drawbridge serving as the only way over a mote followed by chambers where an intruding enemy would be assailed with boiling oil careening down in flames were a very widespread security measure throughout European castles. The inhabitants of a castle, be they a ruthless lord or a good vassal and his family, had the same risks when hundreds of attackers wielding an array of weapons and siege equipment came to the stronghold in hopes of claiming the small kingdom they ruled.
A fief was basically several square miles of land, ruled by a lord whose castle was in the central area of it, scattered with homes of the wealthy knights to whom the lord had given a land deed. The serfs fell in between this all. A serf was the lifelong servant of a wealthy man. A knight typically owned about ten serfs, his lord had twenty in his possession. Life as a serf was extremely disagreeable even by their standards. If you were a serf you would be considered dirt to a lord or lady. Your pay would be nothing and you would work only for the good of the castle. In return you would be allowed to take refuge in the castle, but if you refused to work, then you would most probably be left out of the protection of the lord and be slaughtered by the onslaught of an enemy force. Either way you probably would not live to old age.
Castles were usually covered by disease and moral standards were low. Wars were often devastating to the economy, but wars were essential to the people in power to keep control of the commoners. Fear of a war kept the surfs in the castle and working hard. After a time of peace rebellion always became a reality, so in a way wars kept people in their place and out of trouble. Another reason for wars was the land and resources that were gained if a castle could be successfully seized. Serfs rarely ever moved up the social ladder.