He was compelled to aid Sultan Murad with troops, and during his absence in Asia, apparently in 1374, his eldest son, Andronicus, secured Constantinople, in alliance with the Turkish Sultan's son, also a rebel against his father. By the aid of Murad, Andronicus was seized. He was imprisoned in the tower of Anemas with his wife and his son John, then only five years old. He was to have been blinded, but perhaps in mercy the sight of one eye was not harmed. After two years he was released, and he at once made alliance with the Genoese and with the Sultan Bayezid, and marched to the capital. He caught his father and his brother Manuel, who were at the palace of the Pegé, now the village of Balukli, and sent them with his younger brother Theodore to the prison in which he himself had been confined, "as Zeus," says the historian Ducas, with a classic touch such as the Greeks always delighted to use, "cast his father Kronos and his brothers Pluto and Poseidon into Tartarus." Andronicus entered the city by the Selivri Kapoussi (gate of the Pege), and held the throne for two years and a half. Bayezid urged him to kill his father and brothers, but he would not; and within two years, in some way, as to which the historians—none of whom are strictly contemporary—differ, they escaped, and with the aid of Murad, or Bayezid (for again the dates are doubtful), attacked the city, entered by the gate of S. Romanus, and defeated Andronicus, who was allowed to retire to Selivria as ruler of the adjacent lands. In 1384 Manuel was recognised as heir to his father. These changes were all effected by the aid of the Turks, and of the cities of Genoa and Venice, who, it might seem, gave the city to whom they would; and when John VI. began to repair the walls which thirty-six years before he had himself despoiled, he was stopped by order of Bayezid and compelled to destroy what he had done.

In his time decay visibly laid its hand on the still splendid city. Many of the streets, it is said, were almost in ruins, the palaces empty, and the costliest and most beautiful treasures of the ancient Byzantine art had been sold to the Genoese and the Venetians. But for the defeat of Bayezid by Timur, the prize would have fallen into the hands of the Turks half a century before it was theirs at last.

Manuel II. had an unquiet reign. Forced to yield on every side to the demands of the Sultan, blockaded in Constantinople, he was at last forced to admit his cousin John, the son of Andronicus, as joint Emperor, in 1399, a title which he seems to have borne but a short time.

For a while it seemed that the distractions and defeats of the Turks might give opportunity for a revival of the Empire. In 1411 a Turkish attack on Constantinople was driven off; but the Greeks were incapable of using their own victories or the weakness of their enemies; and though Manuel made some reforms in the administration the members of his household thwarted him on every side. The years of peace were wasted, and in 1422 Murad II. appeared before the walls of the imperial city.

The defeat of the Turks—their last—was soon followed by the death of Manuel (1425). John VII. set himself to repair the walls, but he could not rebuild or repopulate the city. The decay, in spite of the outward splendour, the disgraceful subjection of the Emperor to the Turks, and the hatred of the Greeks for the Westerns, all struck the keen observer Bertrandon de la Brocquière, a Burgundian knight, who visited the city in 1433. The despairing effort of the Emperor was to win the help of a new crusade by union with the Latin Church.

Those who have stood in admiration before the frescoes of Benozzo Gozzoli in the Riccardi Palace at Florence will remember the solemn impressive figure of John Palæologus, in his gorgeous robes, as he rides in the procession of the Magi, a stately personage contrasting markedly with the bourgeois Medici who follow him. Italians knew the Eastern Emperor, for in 1438 he stood with the patriarch before the Council of Ferrara, and in the next year, in Florence itself accepted, with his bishops (save the bishop of Ephesus), the doctrines of the Latins, and joined on July 6, 1439, in the proclamation beneath the dome of Brunelleschi, then only three years completed, of the unity of the Catholic Church of East and West.

When he returned to Constantinople the people refused to accept the union, and even the bishops who had signed the decrees of Florence now repudiated their act as a sin. No help came from the West; and John died in 1448, having preserved his throne even by temporising with the Turks.

Constantine Palæologus was the eldest surviving son of the Emperor Manuel. He could only ascend the throne by the consent of the Sultan, and when that was obtained he was crowned in Sparta, where he had ruled. On the 12th of March 1449 he entered Constantinople. The city was receiving its new lord with exultation and joy, says his friend and chronicler Phrantzes. So long as Murad still reigned they were indeed safe, but when Mohammed II. became Sultan it was clear that there would be war.

Constantine turned—it was his only hope—to the West for aid. He sent an embassy to Rome begging for help, and showing willingness to renew the union of the Churches. The Pope, Nicholas V., sent back Cardinal Isidore, who had once been a Russian bishop, but, having accepted the decrees of Florence, had remained loyal to them, and was an exile from his country in consequence. He arrived at Constantinople in November 1452, bringing some money and a few troops. On December 12, 1452, the union was ratified in S. Sophia, and Cardinal Isidore said mass according to the Latin rite. From that day the people regarded the church as desecrated. In the church and monastery of the Pantokrator the monk Gennadios preached against the crime and folly of the union. Many of the great nobles cried out against it; one even declared that the Sultan would be a far better lord than the Pope. As Constantine rode through the streets daily the mob mocked and reviled him; and some cried out "rather than that we should be Latins would we be Turks." The holy sacrifice of the Body and Blood of Christ they rejected, declaring that it was polluted. Even if an angel from heaven had descended and declared that he would save the city if only the people would unite with the Roman Church the people would have refused. So the chroniclers describe the disunion within. Without, the preparations were complete.

The conquerors of Constantinople had had a romantic history. A horde of barbarians, coming from the far East, and a branch of the race known to Chinese historians as the Hiung-no, they emerge into history in the sixth century, then assuming the name of Turk, which they were to make famous. In the latter half of that century they became known to the rulers of Constantinople. In 568 embassies came to the Emperor from the Northern Turks. Eight years later an embassy was sent to the Southern Turks. At the very end of the century an embassy came to the Emperor Maurice in 598 from the Khan of the Turks, now claiming to be a great sovereign. But it was more than six centuries before the Empire came face to face with the actual tribe which should found the power that was to take its place. Pressed hard by the Seljuks, with territories limited to the Bithynian province, it was not till the beginning of the fourteenth century that Osman, the founder of the Osmanlis, came forward as a leader who should begin a line of mighty sovereigns.