A surprising amount! They were mostly pictorial but the Aztecs and their vassal cities were very meticulous about keeping government records of all kinds and ev

A surprising amount! They were mostly pictorial but the Aztecs and their vassal cities were very meticulous about keeping government records of all kinds and even though almost all of Tenochtitlan's documents were destroyed during the battle, some of them were backed up in other cities. Since the conquistadors spent some time in the city as guests of Montezuma, we've also got first hand accounts from the soldiers and friars.