The term 'Castle SECURITY' can be broken down into two parts: MOAT, which is a four letter word, and SECURITY. A MOAT is a deep, wide ditch that is usually filled with water and surrounds a castle or other fortified structure. It was used to protect the castle from attack by providing an additional layer of defense. The presence of a MOAT also made it difficult for attackers to breach the walls of the castle. In addition to the MOAT, castles also had other SECURITY measures such as guards, watchtowers, and drawbridges.