Mahomet the Unifier died in 1421, and evil days at once set in for Constantinople and for Christendom, when his ambitious son Murad II. came to the throne. Manuel Paleologus was one of the first to feel the change in the times. He tried to make trouble for Murad, by supporting against him two claimants to the Ottoman Sultanate, each named Mustapha, one the uncle, the other the brother of the new ruler. This drew down on the empire the fate which had been delayed since 1370: the Sultan declared war on Manuel, took one after another all the fortresses which had been recovered by the peace of 1403, and finally laid siege to Constantinople. For the last time the walls of the city proved strong enough to repulse an assault. Though Murad levelled against them cannon, then seen for the first time in the East, built movable towers to shelter his troops, and launched his terrible Janissaries to the assault, he could not succeed. The report of a miraculous vision of the Virgin, who vouchsafed to reveal herself as the defender of the city, encouraged the Greeks to resist with a better spirit than might have been expected. At last the pretender Mustapha, whom Manuel had supplied with money to cause a revolt against his brother, began to stir up such trouble in Asia Minor, that the Sultan determined to raise the siege and march against him. He granted Manuel peace, on the condition that he ceded all his dominions save the cities of Constantinople and Thessalonica and the Peloponnesian province. Thus the empire once more sank back into a state of vassalage to the Ottomans [1422]. Manuel II. died three years after, at the age of seventy-seven. He was the last sovereign of Constantinople who won even a transient smile from fortune. The tale of the last thirty years of the empire is one of unredeemed gloom. To Manuel succeeded his son John VI., whose whole reign was passed in peace, without an attempt to shake off the Turkish yoke; such an attempt indeed would have been hopeless, unless backed by aid from without. As Manuel II. once observed, “the empire now requires a bailiff not a statesman to rule it.” Treaties, wars, and alliances were not for him: all that he could do was to try to save a little money, and to keep his walls in good repair, and even these humble tasks were not always feasible.