The retreat being determined upon, it was necessary to decide upon whether it should be carried out by night or by day. If in the daytime the enemy would be more easily resisted, any ambuscades which might be prepared would be more easily avoided, while they could better take precautions to repair any bridges broken by the Mexicans. On the other hand, it was known that the Indians will seldom attack an enemy after sunset, but what really decided Cortes in favour of a nocturnal retreat was, that a soldier who dabbled in astrology had declared to his comrades that success was certain if they acted in the night. They therefore began their march at midnight. Besides the Spanish troops, Cortes had under his orders detachments from Tlascala, Zempoalla, and Cholula, which, notwithstanding the serious losses which had been sustained, still numbered 7000 men. Sandoval commanded the vanguard, and Cortes the centre, where were the cannon, baggage, and prisoners, amongst whom were a son and two daughters of Montezuma; Alvarado and Velasquez de Leon led the rearguard. With the army was carried a flying bridge, which had been constructed to throw over any gaps there might be in the causeway. Scarcely had the Spaniards debouched upon the dike leading to Tacuba, which was the shortest of all, when they were attacked in front, flank, and rear by solid masses of the enemy, whilst from a fleet of numberless canoes, a perfect hailstorm of stones and missiles fell upon them. Blinded and amazed, the allies knew not against whom to defend themselves first. The wooden bridge sank under the weight of the artillery and fighting men. Crowded together upon a narrow causeway where they could not use their fire-arms, deprived of their cavalry who had not room to act, mingled with the Indians in a hand-to-hand combat, not having strength to kill, and surrounded on all sides, the Spaniards and their allies gave way under the ever renewed numbers of the assailants. Officers and soldiers, infantry and cavalry, Spaniards and Tlascalans were confounded together, each defended himself to the best of his ability, without caring about discipline or the common safety.