Some castles contained drawbridges that allowed visitors to enter or keep enemies out of the castle. Drawbridges were usually accompanied by a moat. A moat is a body of water surrounding the castle that was deep and broad to keep unwanted visitors from entering the castle. In some cases the moat may have been "dry," meaning water was not present and it only appeared as a ditch. The drawbridge was lowered by those guards inside the castle when visitors needed to cross the moat.
Castle walls were often high and were built to be between eight and 20 feet wide, foiling any weapons or battering rams attempting to enter the castle. Castle walls were built in many different styles to include straight and curtain walls which inhibited enemies from scaling the outer walls of the structure. Curtain walls were shaped at a downward angle making climbing more difficult and contained crenelations which can be described as the lower sections at the top of the castle walls appearing as raised squares for battle.
Towers were commonly built into the corners of castles for both structural purposes and to defend the kingdom from invaders. Each tower was much taller than the top of the castle walls to allow guards to spot enemies approaching from afar while archers also used the area to keep them at bay. In some cases, towers also held prisoners.
The Keep of a castle was often elevated in the center of the castle and was the area most secure from enemies. Typically, the keep was the center of defense for the kingdom's army and also contained living quarters for the kingdom's most important habitants. It could be described as a castle within the castle and had very strong walls.