A Byzantine castle is a fortified structure built during the Byzantine Empire, which lasted from the 4th to the 15th century. These castles were designed to protect cities and important locations from invasions. They often featured thick walls, towers, and strategic locations on hills or near water to enhance defense. Many Byzantine castles, such as Kastoria and Mystras, showcase unique architectural styles, blending Roman, Greek, and Eastern influences. The castles served not only military purposes but also as administrative centers, housing local rulers and their courts. Today, many of these structures are historical sites, attracting visitors interested in Byzantine history.