Saying this, they gave a signal, and a storm of arrows and javelins pierced the air, and fell into the beleaguered fortress. Notwithstanding the bold tone assumed by Cortez, the Spaniards were in great dismay. It was manifest to all that their destruction was certain unless they could cut their way through the enemy, and escape from the city. The extraordinary energies of this iron fanatic still remained unshaken. Calmly he reflected upon his position, examined his resources, and formed his plans. The Mexicans had barricaded the streets, and had broken down the causeways, to prevent, if possible, the escape of their foes. But there was no longer any alternative for Cortez. Destruction was certain unless he could effect his escape. He decided to make the desperate attempt at midnight. He immediately constructed moving towers, to be pushed through the streets on wheels, at the head of his columns, under the protection of which his soldiers could force their way, and make every bullet accomplish its mission. A platform on the top could be let down, affording a bridge to the roofs of the houses, thus placing the Spaniards on a level with their assailants. The sides of the towers were amply strong to repel darts and arrows. Thus protected from all harm, the sharpshooters could sweep the streets and the house-tops. At midnight the retreat was commenced in three divisions. Sandoval led the van, Alvarado the rear. Cortez took command of the centre, where he placed the distinguished prisoners, among whom were a son and daughter of Montezuma, and several of the high nobles. He also carried with his division the artillery, the baggage, and a portable bridge, ingeniously constructed of timber, to be laid over the breaches in the causeway. In profound silence the army issued from their quarters, and marched firmly along through the smouldering and gory streets. For a little time they advanced unmolested; but the Mexicans were watching their movements, and were silently making dispositions for a tremendous onset. Suddenly the shout of an innumerable multitude and the clash of arms rose fearfully in the dark night air, and from every quarter the natives came rushing on, and stones, javelins, darts, and arrows rattled like hail-stones upon helmet and buckler. Every inch of the way was now contested. The progress of the Spaniards, though slow, was resistless, the cannon and the musketry sweeping down all obstacles.