[Sidenote: The Byzantine sovereigns apply to the West.] Mohammed II. became the Sultan of the Turks A.D. 1451. From the moment of his accession, he turned all his powers to the capture of Constantinople. Its sovereigns had long foreseen the inevitable event, and had made repeated attempts to secure military aid from the West. They were ready to surrender their religious belief. On this principle, the monk Barlaam was despatched on an embassy to Benedict XII. to propose the reunion of the Greek and Latin Churches, as it was delicately termed, and to obtain, as an equivalent for the concession, an army of Franks. As the danger became more urgent, John Palæologus I. sought an interview with Urban V., and, having been purified from his heresies respecting the supremacy of the pope and the double procession of the Holy Ghost, was presented before the pontiff in the Church of St. Peter. The Greek monarch, after three genuflexions, was permitted to kiss the feet of the holy father and to lead by its bridle his mule. But, though they might have the will, the popes had lost the power, and these great submissions were productive of no good. Thirty years subsequently, Manuel, the son and successor of Palæologus, took what might have seemed a more certain course. He travelled to Paris and to London to lay his distress before the kings of France and England; but he received only pity, not aid. At the Council of Constance Byzantine ambassadors appeared. It was, however, reserved for the synods of Ferrara and of Florence to mature, as far as might be, the negotiation. The second son of John Palæologus journeyed again into Italy, A.D. 1438; and while Eugenius was being deposed in the chamber at Basle, he was consummating the union of the East and West in the Cathedral of Florence. [Sidenote: The Greek Church yields to the Latin.] In the pulpit of that edifice, on the sixth of July of that year, a Roman cardinal and a Greek archbishop embraced each other before the people; Te Deum was chanted in Greek, mass was celebrated in Latin, and the Creed was read with the "Filioque." The successor of Constantine the Great had given up his religion, but he had received no equivalent--no aid. The state of the Church, its disorders and schisms, rendered any community of action in the West impossible.