The document discusses the purpose and features of medieval castles, specifically focusing on moats. Moats were deep bodies of water that surrounded castles, protecting them from enemies. They were difficult to wade or swim across, and castle guards could attack any enemies in the water. Moats received water from springs, lakes or rivers, and sometimes contained alligators or crocodiles to further deter intruders. Drawbridges allowed safe entrance to the castle when lowered over the moat as a bridge.