High Quality Content by WIKIPEDIA articles! High Quality Content by WIKIPEDIA articles! Bodrum Castle , located in southwest Turkey in the city of Bodrum, was built by the Knights Hospitaller starting in 1402 as the Castle of St. Peter or Petronium. Confronted with the invasion of Seljuk Turks, the Knights Hospitaller, with their headquarters on the island of Rhodes, needed another stronghold on the mainland. Grand Master Philibert de Naillac 1396-1421 found a suitable site across the island of Kos, where there was already a castle of the Order. This location had been already the site of a fortification in Doric times 1110 BC and of a small Seljuk castle in the 11th century. The same promontory was also the probable site of the palace of Mausolos, the famous king of Caria. The construction of the castle started in 1402 under the German knight-architect Heinrich Schlegelholt. Construction workers were guaranteed a reservation in Heaven by a papal decree of 1409. They used squared green volcanic stone, marble columns and reliefs from the nearby Mausoleum of Maussollos to fortify the castle. The first walls were completed in 1437.