Castel del Monte, a 13th-century citadel located in Andria, Italy, stands as a testament to the ingenuity of medieval architecture. Constructed by Emperor Frederick II during the 1240s, this unique octagonal fortress is celebrated for its geometric precision and classicizing details. Despite its initial appearance as a grand hunting lodge, it was designed with defensive capabilities, including a curtain wall suggested by archaeological findings. Today, Castel del Monte is recognized as a UNESCO World Heritage Site and is featured on the Italian version of the one-cent Euro coin.