Here was the first break in the causeway, and they had brought with them a bridge to lay across it. But here also were some Indian sentinels, who fled in haste on seeing them, rousing the sleeping city with their cries. The priests on the summit of the great temple pyramid were also on the watch, and when the shouts of alarm reached their ears from below, they sounded their shells and beat their huge drum, which was only heard in times of peril or calamity. Instantly the city broke from its slumber, and as the leading Spaniards crossed the bridge a distant sound was heard, which rapidly approached. Soon from every street and lane poured enemies, flinging stones and arrows into the crowded ranks of the Spaniards as they came. On the lake was heard a splashing sound, as of many oars, and the war-cry of a host of combatants broke on the air. A brief interval had sufficed to change the silence into a frightful uproar of sound and the restful peace into the fast growing tumult of furious battle. The Spaniards pushed steadily along the causeway, fighting only to drive back the assailants who landed from their canoes and rushed in fury upon the marching ranks. The horsemen spurred over them, riding them down; the men on foot cut them down with their swords, or hurled them backward with the butts of their guns; the Indian allies of the Spaniards attacked them fiercely, and the roar of war spread far through the gloom of the night. Onward marched the Spaniards, horse and foot; onward creaked and rumbled the artillery and the wagons; and the second canal in the causeway was reached while the rear files were not yet across the first. The Spaniards had made a fatal mistake in bringing with them only one bridge. When the last of the retreating force was across this, a vigorous effort was made to raise it and carry it to the canal in front, but in vain. The weight of men, horses, and cannon had wedged it so firmly in the earth and stones that it could not be moved. Every nerve was strained to lift the heavy mass, until, many of the workmen being killed and all wounded by the torrent of Aztec missiles, they were forced to abandon it. When the dread tidings that the bridge could not be raised spread through the crowded host, a cry of despair arose that almost drowned the sounds of conflict. All means of retreat were cut off. Before them lay a deep and yawning ditch. Behind them pressed an army of assailants. On each side hundreds of canoes dashed on the causeway, yielding foes who rushed in fury upon their crowded ranks. All hope seemed lost. All discipline was at an end. Every one thought only of saving his own life, without regard to the weak or wounded. The leading files, gathered on the brink of the gulf, were pressed forward by the rear. The horsemen in front dashed into the water and swam across, but some of the horses failed to climb the steep and slippery bank, and rolled back with their mail-clad riders headlong into the lake.