Sandoval at the same time advanced along the causeway from Iztapalapan to Coyuhuacan. It was a league and a half in length, and a quarter of a league from shore it passed through an island town, which was captured and burned. Advised of this, Quauhtemotzin directed a fleet to cut the causeway and entrap the Spaniards; but before long two of the vessels were able to relieve Sandoval, who thereupon left a portion of his troops, including the allies, at Coyuhuacan, and joined his chief with the remainder. Nearly a week was occupied in strengthening Fort
Xoloc, arranging the camp, and bringing in supplies, during which time desultory skirmishings were maintained, wherein Sandoval among others received wounds. The brigantines roamed incessantly and inflicted great damage, entering on one occasion for a long distance a canal which led into the suburbs.23 Canoes no longer ventured abroad when a sail was in sight, and the Mexicans began to protect the water approaches and channels with stakes.
In order to complete the investment of the city it was only necessary to occupy the northern causeway to Tepeyacac, along which the besieged maintained a steady intercourse with the mainland. Advised of this neglect by Alvarado, the general ordered Sandoval to form a camp at that town24 with one hundred and forty Spaniards, of whom twenty-three were horsemen, and a full proportion of allies. Alvarado had half as many more infantry and a few more cavalry, while two hundred infantry were quartered at Xoloc, supported besides by a cavalry force in the rear, and by Olid’s party, with whom remained the largest proportion of allies, now over eighty thousand, according to Cortés’ own statement. The fort could not hold them, and they accordingly encamped at Coyuhuacan, which lay more convenient for supplies, and must be occupied to watch the hostile shore and lake towns clustered in this quarter. The brigantines carried at least two hundred and fifty men.25