The parties soon set out for their respective positions. Alvarado and Olid in a little time reached Tacuba. The aqueduct of Chapoltepec passed through this place, affording a supply of fresh water to the Mexican capital. This they determined to destroy, and at once set to the work. The Mexicans opposed them fiercely; the struggle was a hard one, but at length they succeeded in cutting off the pipes. Flushed with success, they now attempted to take possession of the first bridge on the causeway of Tacuba. As they approached this spot, they found immense numbers gathered to oppose them; the causeway was thronged with the enemy, while each side was lined with canoes, from which the Mexicans poured in their arrows. At the first discharge, three Spaniards were slain and thirty wounded. The Spaniards only fought the more fiercely; yet, after all their efforts, they were forced to retreat to Tacuba, eight of their number being dead, and more than fifty wounded. Leaving Alvarado, Olid pushed on to his station at Cojohuacan. In the mean time, Cortes had brought the fleet out on the lake, and after various manœuvres, proceeded to attack a rock near the city, where a large number of the inhabitants had fled for refuge. The Mexicans, perceiving his design, sent out their whole naval force (consisting of four thousand canoes) against his brigantines. Cortes now moved fairly out into the lake, and formed his fleet in the shape of a crescent to receive them. As they came near, the sails of the brigantines were spread, and they dashed through them, overturning some, and scattering the rest, to the great loss of the Mexicans. Olid had now reached his post, and from the temple at Cojohuacan saw the conflict on the lake. He instantly pushed along the causeway toward the city, drove the Mexicans from some of the trenches, and took possession. Cortes now attacked the bastion called Xoloc, situated at the angle made by the junction of the roads of Cojohuacan and Iztapalapan. The Mexicans defended the place with great obstinacy; multitudes fell in their efforts to save it, but it was stormed and taken. As this was a spot of great importance, and in direct communication with the division of Olid, Cortes determined to establish his camp here. The three divisions were now on the three causeways, and, as the principal attacks of the enemy were from the canoes that lined them, he distributed his fleet so as to protect the three divisions in their three efforts against the city--giving orders that they were to be managed in strict obedience to the three officers in command. The siege now regularly commenced.