From Cortés, Third Letter, 270–72

I had, most powerful Sire, in the camp on the causeway two hundred Spanish infantry, amongst whom were twenty-five archers and musketeers, exclusive of the men in the brigantines, who were more than two hundred and fifty in number. In order that we might keep the enemy closely invested, and retain a large number of warriors for our allies, I resolved to enter the city as far as possible, and that the brigantines should afford us their support on both sides of the causeway. I also directed some of the horse[men] and foot[soldiers] from the division at Cuyoacan should repair to the camp, that they might enter with us and that ten horsemen should be left at :the end of the causeway, as a support to our troops. But some of the allies left at Cuyoacan had rebelled and espoused the cause of the city, amongst whom were the inhabitants of the cities of Suchimilco, Culuacan, Iztapalapa, Chilobusco, Mexicalcingo, Cuitaguacad, and Mizquique, all of which lie upon the lake. These seeking to attack us in the rear, I ordered ten or twelve horse[men] to guard the causeway, and as many more to remain at Cuyoacan, together with more than ten thousand of our allies. I also ordered Pedro de Alvarado to attack the city from their posts at the same time in order that I might gain as much as possible on my side.

Having thus made my arrangements, I sallied forth in the morning from the camp, and marched on foot toward the city. We soon found the enemy in defense of a breach that had been made in the road, as wide as the length of a lance, and of the same depth, where they had formed an entrenchment. Here an action ensued, in which valor was shown on both sides. At length we prevailed, and pursued our route along the causeway until we arrived at the entrance of the city, where stood a tower of idols, and near its base a very large bridge that was raised, under which a broad street of water passed, defended by a strong entrenchment. As soon as we reached this place, the enemy began to attack us; but as the brigantines were on both sides of the road, we carried the entrenchment without loss, which we could not have done unless aided by the brigantines. When the enemy began to abandon the ground, the people in the brigantines disembarked, and we passed over the water by means of them, together with the allies from Tlaxcala, Guajocingo, Calco, and Tesaico, in all more than eighty thousand men. While we were employed in filling up with stone and brick the breach made by the destruction of the bridge, the Spaniards gained another entrenchment on the principal and widest street in the whole city. As it contained no water, the entrenchment was easily carried. They then pursued their route along the street until they arrived at another bridge, which the enemy had raised, excepting only one piece of timber, over which they passed. Having reached a place of safety, rendered secure by the intervention of water, they immediately took away the beam. On another part of the ground adjoining the bridge on the opposite side, the enemy had constructed another large entrenchment of clay and unburnt bricks. When we reached this spot, we were unable to cross without throwing ourselves into the water, and this was attended with great danger, as the inhabitants fought with resolute valor. On both sides of the street there was an immense multitude who attacked us in a courageous manner from the terraces: but when a number of our archers and musketeers arrived, and we discharged the two cannon so as to rake the street, we did them great mischief.

[This chapter of the letter continues by explaining how the Spaniards could enter the city but then had to flee, as the Mexicas threw arrows at them from rooftops. Cortés saw only one solution: burn the city down, so there will be no more houses with roofs.]