On through the blackness, shrouding the long avenue of Tlacopan, moved the retreat. Here they stumbled over the corpse of some dead Aztec, there they could distinguish the dark heaps of slain marking some fiercely contested point of the recent fighting. To their excited imaginations it seemed as though these must rise up and betray them. The shadowy ruins of fire-scathed buildings seemed again peopled with flitting forms, and, as they crossed one after another of the canals, the ebon water seemed alive with swarming paddles. But they passed on as unmolested by the living as by the dead, until at length a lighter space between the buildings in front of them announced to the van-guard that the causeway was at hand. As they drew aside to allow the men of Margarino room in which to advance and place their bridge, they felt that the worst of the perilous retreat was over, and could hardly restrain the shouts that would have proclaimed their joy.
Suddenly a shrill cry, chilling the blood in their veins, rose from close beside them. There was a sound of flying footsteps, and the alarm was echoing and re-echoing through the wind-swept streets with an ever-increasing clamor. The priests, watching their fires on top of tall teocals, caught the cry of the flying sentinels and spread the alarm with sounding blasts upon their conch-shells. Now, from the desolated heights of Huitzil's temple, the solemn booming of the great serpent drum, only sounded in times of gravest moment, vibrated through the remotest comers of the city and far out over the waters surrounding it. Red beacon flames sprang from the top of every temple, warning the whole valley that the time of the crisis had come.
"Tlacopan! Tlacopan!" was shouted in frenzied tones through every street and into every house of the sleeping city, and this single word named the rallying point.
With desperate haste Margarino and his men laid their bridge. No longer was there need of silence or concealment. Flight, instant and rapid, was the sole animating thought of the whole army. Sandoval, on prancing Motilla, was the first to test its strength, and after him streamed the eager troops. To the vanguard hastening forward without opposition, safety still seemed within reach; but to the rear, impatiently awaiting the movement of those before them, the night was filled with ominous rushings and sounds denoting the gathering of a mighty host. By the fitful glare of the lofty beacons, now streaming through the upper darkness from all parts of the city, they caught glimpses of hurrying forms and glintings of angry weapons. Mesa's grim gunners blew the matches, kept dry beneath their cloaks, into brighter flame and chuckled hoarsely as they thought of the havoc their falconets would make when once turned loose.
The advanced guard had crossed the bridge and the dense squadrons of the centre, with the heavy guns, ammunition wagons, baggage, treasure, prisoners, and wounded, were passing it when the storm broke. First a few stones and arrows rattled on the mail of the cavaliers, or pricked the naked Tlascalans. Then the dark waters of the lake were smitten by the dip of ten thousand angry paddles, as though by the fierce breath of a whirlwind. The sprinkle of stones and arrows increased to a tempest of hissing missiles. The dark lines of on-rushing canoes dashed against the very rocks of the causeway, while their occupants, leaping out, threw themselves, with reckless ferocity, upon the retreating troops. The shrieks of wounded and dying men began to rise from the hurrying column and the despairing cries of others, overthrown and dragged to the canoes. Above all and drowning all, rose the shrill, exultant yell of "Tlacopan! Tlacopan!" made, for the time being, the Aztec war-cry and taken up by a myriad of fresh voices with each passing minute.
From the distant rear came the roar of Mesa's guns. There the cowardly enemy will be checked at any rate! But they are not. No longer do belching cannon nor levelled lances possess any terror for those whom the war-like Cuitlahua leads to battle.
As hundreds were mowed down by the storm of iron balls, thousands leaped into their places. So irresistibly furious was the Aztec advance that ere the deadly falconets could be reloaded, Mesa, his men, and his guns, were overwhelmed, and swept out of sight, as though beneath the overpowering mass of an alpine avalanche. Alvarado and his handful of cavaliers, who had charged again and again into the fiercely swelling tide of foemen, supporting the guns as long as any were left, now turned, and fled across the narrow bridge.
While these events were taking place with frightful rapidity in the rear, the advance had reached, and were halted by, the second opening in the causeway. Galled by the incessant attacks of their swarming adversaries, and with their own swords rendered well-nigh useless by the cramped space into which they were crowded, these sent back message after message imploring Margarino to hasten forward with the bridge. But the bridge would never be brought forward. Its timbers had become so wedged among the stones of the causeway, by the weight of ponderous guns and mail-clad troops, that not all the efforts of Margarino's sturdy men could move them. Desperately they tugged and strained, but in vain. The bridge was as immovable as the causeway itself. Even as they fulfilled their pledge never to move forward without the bridge, the exulting foe leaped upon them. For a few minutes there was a fierce conflict. Then the seething Aztec flood rolled on, sweeping over Margarino and his men, as it had over Mesa and his guns.