The Knights of St. John, or Knights Hospitallers, had captured
Rhodes in the early 14th century after the loss in 1291 of
Acre, the last
Crusader stronghold in Palestine. From Rhodes, they became an active part of the trade in the
Aegean Sea, and at times harassed Turkish shipping in the
Levant to secure control over the eastern
Mediterranean. A first effort by the Ottomans to capture the island was repulsed by the order in 1480, but the continuing presence of the knights just off the southern coast of
Anatolia was a major obstacle to Ottoman expansion. An
earthquake shook the island in 1481. After the siege and earthquake, the fortress was greatly strengthened against artillery according to the new school of
trace italienne. In the most exposed land-facing sectors, the improvements included a thickening of the main wall, doubling of the width of the dry ditch, coupled with a transformation of the old
counterscarp into massive outworks (
tenailles), the construction of
bulwarks around most towers, and
caponiers enfilading the ditch. Gates were reduced in number, and the old
battlement parapets were replaced with slanting ones suitable for artillery fights. A team of masons, labourers, and slaves did the construction work, with the Muslim slaves charged with the hardest labour. Piri,
Çoban and
Kurtoğlu participated in the divan meetings, and Piri urged the Sultan to hurry to Rhodes. He then went to war with the Sultan. ==Invasion==