Castles: Since the power and security of a lord depended upon his ability to defend himself, fief owners began to build sturdy castles. Castles were designed to withstand a siege and to mount a defense.
At first castles were made of wood. But they were too easy to burn down. By 1100 CE, castles were built of stone. Thick walls surrounded a castle. Inside these thick walls, there were many buildings.
At the first sign of trouble, the commoners rushed to get inside the castle walls before the gates closed and shut them out.
Location: Castles were usually built on top of a hill, if one was handy. That way, the lookout guards could more easily spot attackers approaching.
The Moat: A moat was built around many of the castles. This was a deep ditch surrounding the castle walls, filled with water. A bridge was built to cross the moat. The bridge was raised during an attack. The moat was loaded with traps and sharp spikes in case someone tried to swim across.
The Drawbridge: The drawbridge was the bridge built across the moat. This bridge could be raised and lowered for added protection from intruders.