Bodrum Castle is a historical fortification located in southwest Turkey in the port city of Bodrum, built from 1402 onwards, by the Knights of St John as the Castle of St. Peter or Petronium. A transnational effort, it has four towers known as the English, French, German, and Italian towers, bearing the names of the nations responsible for their construction. The chapel was built around 1407 and the first walls completed in 1437. The castle started reconstruction in the late 14th century, only to be taken over by the Islamic Ottoman Empire in 1523. The chapel was converted to a mosque, and a minaret was added. The castle remained under the empire for almost 400 years. After remaining empty following World War I, in the early 1960s, the castle became the home for the Bodrum Museum of Underwater Archaeology. In 2016 it was inscribed in the UNESCO Tentative list of World Heritage Sites in Turkey.

Bodrum is a municipality and district of Muğla Province, Turkey. Its area is 650 km2, and its population is 192,964 (2022). It is a port city at the entrance to the Gulf of Gökova. Known in ancient times as Halicarnassus, the city was once home to the Mausoleum at Halicarnassus, also known as the tomb of Mausolus, one of the Seven Wonders of the Ancient World.