History of the Deeds of David, King of the Indies
In 1221, in the heat of the Fifth Crusade, intelligence relayed from Bohemond IV, ruler of the crusader state of Antioch, to Jacques de Vitry, preacher and crusade propagandist, reaches crusaders anxiously waiting in Damietta. The intelligence, a report written in Arabic obtained from traveling spice merchants in Antioch, details the westward military progression of a certain King David, purportedly the great-grandson of the famed Prester John, a military leader who, rumor has it, has systematically destroyed Muslim armies in the east.
From Silverberg, The Realm of Prester John:
“During this dismal adventure [the Fifth Crusade], one of the Latin invaders managed to find some good news to send back to Europe. He was Jacques de Vitry, Bishop of Acre, a French prelate who had come to the Near East just before the launching of the Fifth Crusade, and who had been one of [Cardinal] Pelagius’ chief supporters in the dispute with King John of Jerusalem. In the spring of 1221 this bishop relayed hopeful and happy tidings in letters he sent to Pope Honorius, to King Henry III of England, to Duke Leopold of Austria, and to his former colleagues at the University of Paris. ‘A new and mighty protector of Christianity has arisen,” Jacques de Vitry announced. ‘He is King David of India, who has taken the field of battle against the unbelievers at the head of an army of unparalleled size.’This King David was a Christian, the bishop reported, and was either the son or the grandson of Prester John—although, Bishop Jacques pointed out, “King David was himself commonly called Prester John.” His kingdom was deep in Asia. His involvement in the affair of the Near East had come about because the Caliph of Baghdad had been threatened with war by a fellow Moslem prince, the Shah of Khwarizm; seeing no other ally at hand, the caliph had requested the Nestorian Catholicos—or Patriarch—of Baghdad to summon King David to his aid, and the king had agreed to defend the caliph against the Khwarizmians” (71).
For a close account of the entire Fifth Crusade, see Powell.