On April 6th Sultan Mahomet II encamped on the slope of the hill facing the quarter of Blachern, a little beyond the ground occupied by the crusaders in 1203, and immediately ordered the construction of lines extending from the head of the port to the shore of the Propontis. These lines were formed of a mound of earth, and they served both to restrain the sorties of the besieged and to cover the troops from the fire of the enemy's artillery and missiles. The batteries were then formed; the principal were erected against the gate of Charsias, in the quarter of Blachern, and against the gate of St. Romanus, near the centre of the city wall. It was against this last gate that the fire of the monster gun was directed and the chief attack was made. The land forces of the Turks probably amounted to about seventy thousand men of all arms and qualities; but the real strength of the army lay in the corps of janizaries, then the best infantry in Europe, and their number did not exceed twelve thousand. At the same time, twenty thousand cavalry, mounted on the finest horses of the Turkoman breed, and hardened by long service, were ready to fight either on horseback or on foot, under the eye of their young Sultan. The fleet which had been collected along the Asiatic coast, from the ports of the Black Sea to those of the Aegean, brought additional supplies of men, provisions, and military stores. It consisted of three hundred twenty vessels of various sizes and forms. The greater part were only half-decked coasters, and even the largest were far inferior in size to the galleys and galeases of the Greeks and Italians. The fortifications of Constantinople toward the land side vary so little from a straight line that they afford great facilities for attack. The defences had been originally constructed on a magnificent scale and with great skill, according to the ancient art of war. Even though they were partly ruined by time and weakened by careless reparations, they still offered a formidable obstacle to the imperfect science of the engineers in Mahomet's army. Two lines of wall, each flanked with its own towers, rose one above the other, overlooking a broad and deep ditch. The interval between these walls enabled the defenders to form in perfect security, and facilitated their operations in clearing the ditch and retarding the preparation for assault. The actual appearance of the low walls of Constantinople, with the ditch more than half filled up, gives only an incorrect picture of their former state.