Pierre d' Aubusson, grand master of the hospitallers, or knights of St. John of Jerusalem, born at La-marche, France, in 1423, died in 1503. He is said to have first served in the Hungarian armies against the Turks. In 1444 he accompanied the dauphin, afterward Louis XL, in his campaign against the Swiss. He next repaired to the island of Rhodes, where he was admitted as a knight of St. John. He soon became a prominent member of the order, and on the death of the grand master Des Ursins he was unanimously elected his successor. When Mohammed II. threatened Italy, D'Au-busson had Rhodes strongly fortified, at the same time forming an alliance with the bey of Tunis and sultan of Egypt. Mohammed sent against Rhodes a fleet of 160 sail, carrying an army of 100,000 men, under the command of the apostate Misach PalaBologus (Messih Pasha). The Turks invested the town of Rhodes at the end of May, 1480. D'Aubusson, who made an admirable defence, was so severely wounded that his life was despaired of; but he compelled the Turks to raise the siege after two months. He now became active in the intrigues that troubled the court of Constantinople. He received at Rhodes Zizim or Jem, the brother of Sultan Bajazet, who became in his hands a powerful instrument of influence on the Turkish court.

Zizim was first transferred to France, then delivered to Pope Innocent VIII., who rewarded D'Aubusson with the title of cardinal and the office of legate of the holy see in Asia. But the failure of a plan he had long cherished for the union of Europe against the Turks, together with other disappointments, caused him to retire from affairs, and his last years were spent in Rhodes.