A citadel is a fortified structure or stronghold designed to protect a city or important area from attacks. Typically built on elevated ground, citadels serve as a last line of defense during sieges. They often include thick walls, towers, and sometimes a moat, making them difficult to breach. Historically, citadels were essential in military strategy, providing a safe haven for civilians and soldiers alike. Many ancient civilizations, such as the Romans and Byzantines, constructed citadels to safeguard their territories. Today, some citadels have been preserved as historical sites, showcasing architectural styles and military history.