To establish an easy and rapid communication between the naval camp on the Bosporus and the army before Constantinople, Mahomet ordered a floating bridge to be constructed across the port, from the point near the old foundry, on the side of Galata, to that near the angle of the city walls, near Haivan Serai, the ancient amphitheatre. The roadway of this bridge was supported on the enormous jars used for storing oil and wine, numbers of which were easily collected in the suburbs of Galata. These jars, when bound together with their mouth inverted in the water, formed admirable pontoons. Artillery was mounted on this bridge and the galleys were brought up to the city walls, which were now assailed from a quarter hitherto safe from attack. The Genoese under Justiniani on one occasion, and the Venetians on another, were defeated in their attempts to burn the Turkish fleet and destroy the bridge. The fire of the artillery rendered the attacks of the Italians abortive, and their failure afforded a decisive proof that the defence of the city was becoming desperate. To avoid the admission of their inferiority in force, the defeated parties threw the blame on one another, and their dissensions became so violent that the Emperor could hardly appease the quarrel. During all the labors of the besiegers in other quarters, the approaches were pushed vigorously forward against the land wall. Though the activity in other and more novel operations might attract greater attention, the industry of those engaged in filling up the ditch, and the fire of the breaching batteries, never relaxed. Though all attempts to cross the ditch at the gate of St. Romanus were long baffled by the Greeks, and the mining operations at Blachern were discovered and defeated by Johann Grant, still the superior number and indefatigable perseverance of the Ottomans at last filled up the ditch, and the fire of their guns ruined the walls. A visible change in the state of the fortifications encouraged the assailants, and showed the besieged that the enemy was gradually gaining a decided advantage. At the commencement of the siege, the Ottoman engineers had displayed so little knowledge of the mode of using artillery to effect a breach that a Hungarian envoy from John Hunyady,[1] who visited Mahomet's camp, ridiculed the idea of their producing any effect on the walls of Constantinople. This stranger was said to have taught the Turks to fire in volleys, and to cut the wall in rectangular sections, in order to produce a practicable breach.