From Díaz del Castillo, Vol. 2, Chapter 126

... so we went towards the Great Temple to their Idols. Then, all of a sudden, more than four thousand Mexicas ascended it, not counting other Companies that were posted on it with long lances and stones and darts, and placed themselves on the defensive, and resisted our ascent for a good time, and neither the towers nor the cannon or crossbows, nor the muskets were of any use nor the horsemen, for although they wished to charge [on] their horses, the whole of the courtyard was paved with very large flagstones, so that the horses lost their footing, and they were so slippery that they fell. While from the steps of the Great Temple they halted our advance, we had so many enemies on one side and the other that although our cannons carried off ten or fifteen of them and we slew many by swords and charges, so many men attacked us that we were not able to ascend the Great Temple. However with great unanimity we persisted in the attack and without taking the towers we made our way to the summit.

Here Cortés showed himself very much of a man, as he always was. Oh! what a fight and what a fierce battle took place; it was a memorable thing to see us all streaming with blood, and covered with wounds and others slain. It pleased our Lord that we reached the place where we used to keep the image of Our Lady, and we did not find it, and it appears, as we soon learned that the great Moctezuma paid devotion to Her, and ordered it to be preserved in safety.

We set fire to their Idols and a good part of the chamber with the Idols Huitzilopochtli and Tezcatlipoca was burned. On that occasion the Tlaxcalans helped us a lot. After this was accomplished, while some of us were fighting and others tending the fire, as I have related, oh to see the priests who were stationed on this Great Temple, and the three or four thousand Indians, all men of importance!

While we descended, oh how they made us tumble down six or even ten steps at a time! And so much more there is to tell of the other squadrons posted on the battlefield and recesses of the Great Temple discharging so many darts and arrows that we could face neither one group of squadrons nor the other.

We resolved to return to our quarters with much toil and risk to ourselves, our fortresses being destroyed, all of us wounded and sixteen slain with the Indians constantly pressing on squadrons on our flanks.

However clearly I may tell all this, I can never explain it to any one who did not see us. So far, I have not spoken about what the Mexican squadrons did who kept attacking our quarters while we were marching outside, and the great obstinacy and tenacity they displayed in forcing their way in.

Many times I have seen among the Mexicas and Tlaxcalans paintings of this battle, and the assault on the Great Temple, as they look upon it as a very heroic deed. And although the pictures that they have painted depict all of us as badly wounded and with blood and many of us dead they considered it a great feat, this setting fire to the Temple ...