Nevertheless the strength of the continuous wall outside of Thrace, flanked with towers and bristling with battlements, the great thickness and the height of the walls, the site and depth of the trenches, the cincture of the waves, the impregnable renown of the city, the history of the numerous and fruitless sieges which Constantinople had withstood did not leave Mohammed and his generals at ease as to the result. Twenty-nine times since its foundation had this mistress of the seas and of the continents seen an enemy under its walls. Constantinople had triumphed in twenty-one. Then any day the West might relieve the city through the two seas. Mohammed was looking ceaselessly towards the sea dreading to see approach through the Dardanelles a cloud of Christian sail bringing the courage and skill of Europe to the battlefield of Christendom. Oh that the wasted warriors of Jerusalem might spring to life again and save Europe from the curse of Islam. But there was no voice, neither any that regarded. Constantinople was left alone in her death agonies. The Turkish vanguards soon swept away the towns and villages as far as the gates of the city and Mohammed and his army halted at the distance of five miles. Thence ordering the final disposition of his vast army he marched in battle array, planted the imperial standard before the gate of St. Romanus and on the 6th of April, 1453, formed the memorable siege of Constantinople. The colossal cannon of Adrianople and some others of very great size were trained upon this single gate, while eighteen other batteries were placed in a continuous line along the main wall. On the morning of the 7th at break of day the fire opened from all these volcanoes and the first great siege conducted with the help of heavy artillery had begun. The tactics of the Hungarian officer were first to batter over a large area the ramparts of the gate of St. Romanus and then to shatter the center with the fire of the great guns. The charge of the great cannon of Urban was five hundred pounds of powder--the ball like a mass of rock hurled from a crater on fire made the very ground tremble beneath the walls. The entire facings of the towers and the bastions crumbled into the moat. Thus during ten days, while keeping his soldiers behind the eminences of the ground only as necessary to work the batteries, did Mohammed watch the breaches being made by the cannon of Urban in the walls, towers and gates of Constantinople. But two hours and tons of oil were scarce sufficient to cool the bronze gun, and only seven or eight shot could be discharged a day: but each of these rent the walls like an earthquake. On the tenth day the great gun burst with terrific force, hurling the dismembered bodies of its inventor and the gunners far over the walls into the doomed city.