The headquarters of the Knights Hospitaller were on the island of Rhodes. In 1402 their fortifications at İzmir fell to the Mongols under Tamerlane. Threatened by an invasion of the Seljuks they built the castle at Bodrum. Its location was the site of a fortification during the Doric Greek period. There was also a small Seljuk castle in the 11th century. The same promontory is also the probable site of the palace of Mausolos. He was the king of Caria. The construction of the castle began in 1404. It was fully fortified by 1460. Bodrum came under its final siege in 1522. At the time it was still strong enough to send men to Rhodes. After Rhodes fell, the castle surrendered.