One of the first expeditions undertaken by the new sultan was the siege of Constantinople (1422), but the fortune rather than the genius of the Emperor Manuel prevented the attempt. Amurath was recalled to Asia by a domestic revolt, and the siege was raised. While the sultan led his Janizaries to new conquests, the Byzantine Empire was indulged in a servile and precarious respite of thirty years. Manuel sank into the grave, and John Palæologus II. (1425-1448) was permitted to reign for an annual tribute of 300,000 aspers and the dereliction of almost all that he held beyond the suburbs of Constantinople. On November 1, 1448, Constantine, the last of the Roman emperors, assumed the purple of the Cæsars. For three years he was allowed to indulge himself in various private and public designs, the completion of which were interrupted by a Turkish war, and finally buried in the ruins of the empire. _IV.--The Great Siege of Constantinople_ Mahomet II. succeeded his father Amurath on February 9, 1451. His hostile designs against the capital were immediately seen in the building of a fortress on the Bosphorus, which commanded the source whence the city drew her supplies. In the following year a quarrel between some Greeks and Turks gave him the excuse of declaring war. His cannon--for the use of gunpowder, for some time the monopoly of the Christian world, had been betrayed to Amurath by the Genoese--commanded the port, and a tribute was exacted from all ships that entered the harbour. But the actual siege was delayed until the ensuing spring of 1453. Mahomet, in person, surveyed the city, encouraged his soldiers, and discussed with his generals and engineers the best means of making the assault. By his orders a huge cannon was built in Hadrianople. It fired a ball one mile, and to convey it to its position before the walls, a team of sixty oxen and the assistance of 200 men were employed. The Emperor Constantine, unable to excite the sympathy of Europe, attempted the best defence of which he was capable, with a force of 4,970 Romans and 2,000 Genoese. A chain was drawn across the mouth of the harbour, and whatever supplies arrived from Candia and the Black Sea were detained for the public service. The siege of Constantinople, in which scarcely 7,000 soldiers had to defend a city sixteen miles in extent against the powers of the Ottoman Empire, commenced on April 6, 1453. The last Constantine deserves the name of a hero; his noble band of volunteers was inspired with Roman virtue, and the foreign auxiliaries supported the honour of the Western chivalry. But their inadequate stock of gunpowder was wasted in the operations of each day. Their ordnance was not powerful either in size or number; and if they possessed some heavy cannon, they feared to plant them on the walls, lest the aged structure should be shaken and overthrown by the explosion.