Aided in this manner, the soldiers were able to advance along the several dikes, until they got possession of certain military stations, on each, which might have been called the gates of Mexico. It has been already said, that the causeways of Iztapalapan and Cojohuacan, coming respectively from the south and southwest, united together at the distance of less than a league from Mexico. At the point of junction, the causeway expanded into a mole or quay, where was a strong and lofty stone wall, the passage through which was contrived by the overlapping of the walls, in the manner described at Tezcuco. This rampart was defended by very strong towers and by a parapet with embrasures, from which the defenders could easily repel any enemy, inferior in strength and determination to the Spaniards. The point was called Xoloc, and when wrested from the hands of the Mexicans, became the head-quarters of Cortes. A similar expansion of the dike of Tacuba, fortified in the same way, and at the distance of two miles from the city, and one from the shore, afforded a resting-place and garrison for the forces under Alvarado, whose first act, after reaching Tacuba, was to destroy the aqueduct of Chapoltepec, which consisted of a double line of baked earthenware pipes, carried across the lake on a dike constructed only for that purpose, and therefore so narrow and inconsiderable, that it does not appear that the Spaniards derived any advantage from the possession of it. The division of De Olid united with that of Sandoval at the point Xoloc; the latter of whom was afterwards directed to take possession of the northern dike of Tepejacac, the remains of which may yet be traced between the city and the hill of Our Lady of Guadalupe, on which was a fortification resembling the others. These positions being thus assumed, the Captain-General divided the fleet of brigantines among the three captains, to whom they were of vast service, by protecting the flanks of their divisions. From this period, the siege may be considered to have been begun in form; and it was continued with a fury of attack and resistance almost without parallel in the history of conquest. Foot by foot, and inch by inch, the invaders advanced, staining the causeways with their blood, and choking the lake with the bodies of their foes. Ditch after ditch was won and filled, and almost as often lost and re-opened. The day was devoted to battle, the night to alarms. The only periods of rest were when the daily tempests, for it was now the heart of the rainy season, burst over the heads of the combatants, as if heaven had sent its floods to efface the horrible dyes of carnage, and its thunders to drown the roar of man's more destructive artillery. Then, the exhausted soldier and the fainting barbarian flung themselves to rest upon the trodden mud of their ramparts, within sight of each other, regardless of the wrath of the elements, so much less enduring than their own.