Answer:
Although most Crusader States had been retaken by Muslims centuries earlier, the Knights Hospitaller, a crusading order, continued to exist. In fact, their presence on the island of Rhodes made Rhodes the last Crusader State still standing. The Knights Hospitaller had made it their headquarters after taking it from the Byzantines in 1310, who had in turn captured the island during the First Crusade.
The Knights harassed Ottoman shipping, and the Ottomans knew their piracy would remain a threat unless removed. In 1520, Sultan Selim I died, and was succeeded by Suleiman “The Magnificent.” Suleiman was determined to put an end to the Knights’ presence on his doorstep.
However, Suleiman knew this would not prove easy. The Ottomans had already tried to take Rhodes once, in 1480, without success. The 1480 assault was utterly crushed despite the Muslims outnumbering the Christians probably by at least ten to one. Suleiman expected a hard fight, and prepared accordingly.
The Knights’ fortress was incredibly well defended, and was possibly the most secure fortress in Christendom. It had multiple rings of thick stone walls on all sides except for a harbor, as well as the natural advantages of the island. The walls included protruding bastions that could be used to attack anyone approaching the walls from multiple sides.
However, there were only around 700 Knights on the island. When the Grand Master of the Order, Philippe Villiers de L’Isle-Adam, learned of the impending attack, he sent out requests for aid. However, only a small number of Venetians from nearby Cyprus joined. Rhodes had around 6,700 defenders when the Ottoman army arrived with nearly 200,000 men on 400 ships.
Suleiman himself soon arrived to directly oversee the attack. Although the Knights were badly outnumbered, they had made preparations for a siege. They had harvested or destroyed all of the wheat on the island so there would be no food for their invaders, and they placed a giant chain across the harbor so that nobody could enter it.
The Ottomans began a massive bombardment with their cannons, but the walls generally held up well. However, Suleiman had another trick up his sleeve. He brought a number of sappers, men whose job it was to dig under the walls to plant gunpowder charges.
Suleiman himself soon arrived to directly oversee the attack. Although the Knights were badly outnumbered, they had made preparations for a siege. They had harvested or destroyed all of the wheat on the island so there would be no food for their invaders, and they placed a giant chain across the harbor so that nobody could enter it.
The Knights had planned for this, too. They set up a system to detect vibrations coming from the earth, and would target tunnels before they could be used to bring down the walls. The defenders destroyed over 50 tunnels this way.
However, on September 4, after months of digging, the Ottomans successfully detonated two mines under the wall. This explosion also damaged the moat, since sections of the wall filled in part of it.
With a 12 yard (11 meter) hole blown in the wall, the Ottoman infantry launched an assault. Although they took a section of wall, a counter-attack led by Grand Master L’Isle-Adam himself forced them back. The Ottomans made several more attacks, but all were forced back.
