But the Spaniards had yet to learn to their cost the lengths of Aztec tenacity and ferocity. It will be recollected that the city was connected to the lake shores by means of four causeways, built above the surface of the water; engineering structures of stone and mortar and earth, which had from the first aroused the admiration of the Spaniards. These causeways, whilst they rendered the city almost impregnable from attack, were a source of weakness in the easy cutting-off of food supplies, which they afforded to the enemy. A simultaneous assault on all these approaches was organised by the Spaniards, under Sandoval, Alvarado, and Cortes himself, respectively, whilst the brigantines, with their raking artillery, were to support the attack by water, aided by the canoes of the Tlascalan and Texcocan allies. A series of attacks was made by this method, and at last the various bodies of Spaniards advanced along the causeways and gained the city walls. But frightful disaster befel them. The comparative ease with which they entered the city aroused Cortes's suspicions; and at that moment, from the summit of the great _teocalli_, rang out a fearful note--the horn of Guatemoc, calling for vengeance and a concerted attack. The notes of the horn struck some ominous sense of chill in the Spaniards' breasts, and the soldier-penman, Bernal Diaz, who was fighting valiantly there, says that the noise echoed and re-echoed, and rang in his ears for days afterwards. The Spaniards on this, as on other occasions, had foolishly neglected to secure the breaches in the causeways as they passed, or at least the rash Alvarado had not done so with his command, his earlier lesson unheeded; and when the Christians were hurled backwards--for their easy entrance into the great square of the city had been in the nature of a decoy--disaster befel them, which at one moment seemed as if it would be a repetition of that of the _Noche Triste_. "The moment I reached that fearful bridge," Cortes wrote in his despatches, "I saw the Spaniards returning in full flight." Remaining to hold the breach, if possible, and cover the retreat, the chivalrous Cortes almost lost his life from a furious attack by the barbarians in their canoes, and was only saved by the devotion of his own men and Indian allies, who gave their lives in his rescue. Word, nevertheless, had gone forth among the men that Cortes had fallen; and the savages, throwing before the faces of Alvarado and Sandoval the bloody heads of decapitated Spaniards, cried tauntingly the name "Malintzin," which was that by which Cortes was known among the Mexicans. Men and horses rolled into the lake; dead bodies filled the breaches; the Christians and their allies were beaten back, and "as we were all wounded it was only the help of God which saved us from destruction," wrote Bernal Diaz. Indeed, both Cortes and the Spaniards only escaped, on these and other occasions, from the Aztecs' desire to take them alive for sacrifice.