An interesting part of this historical document is how it shows the Aztecs explaining their religion and culture and trying to preserve everything that remained of it side by side with the invading colonist's efforts to use that information to figure out how to brainwash them and destroy everything they've just learned about. After describing the Aztec gods, at the end of the first book the Spanish missionaries threaten to subject anyone to "the most extreme torments" for not reporting an Aztec who practices their native religion or participates in any of their traditions. The Catholic Church even went as far as to ban tamales and amaranth. After tricking them into revealing all the details of their religion and traditions so that they could convert them more easily, the Christians decided that every one of the Aztec gods was a demon and organized the torture and collective murder of anyone who prayed to them or participated in any activity that remotely resembled Aztec traditions of any kind. Luckily they didn't fully succeed because a lot of the culture, especially the food and art, still remains part of Mexican culture today.

In describing Aztec rituals and ceremonies in book two, the Spanish made sure to make them sound as cruel as possible, intentionally focusing on their more violent traditions, but you can't trust the Spaniards to give an accurate, unbiased account because it's clear throughout their translation that they're making a point of being as ethnocentric as possible and finding ways to negative interpret everything that the Aztecs ever did. Child sacrifices weren't as prevalent in Aztec culture as the Spanish wanted their fellow countrymen to believe, and even if it were that's none of their business and the atrocities committed against the Aztecs by Spain far exceed anything the Aztecs ever did to anybody. The Aztecs may have been brutal in war and slavery, but at least they didn't exterminate full continents and erase thousands of years of rich cultural history. By all accounts the Inquisition was much more brutal and terrible than anything that ever happened in the Aztec Empire. The Inquisition itself and the pogroms and witch hunts in Europe were all ritual mass sacrifices with exponentially more sacrificial victims, including hundreds of thousands of children. So the Spaniards had absolutely no right to judge the Aztecs for having their own ritual sacrifices of mostly prisoners. Even today too many people still believe in the lies and exaggerations that the invading Spanish barbarians told Europeans about the Aztecs, and somehow consider their extermination justified. Instead of conquering them they could have established trade between the empires and things would have been a lot better for everyone.

There is an amusing part of book ten where the Spanish side is giving instruction to the Catholic Church on how to brainwash the Aztecs with Christianity, while the Nahuatl side is describing every part of the human body. I don't know if it's just the translation but it's kind of like modernist literature. Here is a description of a tooth:

"The tooth is a bone whitewhitewhiteyellowyellowlike ripe maize maize-dough-colored very white like a seashell darkenedblackvaricoloredstained with cochineal stainedlongsmallminutelong and thinthickroundroundroundlike a spindle whorl pointedeach one pointedwidecomb-likecomb-likewigglingwigglingbroken decayeddecayedrottensmutty blotcheddirtydirtyscummywith thick scum of decayed root long and thin at the root it bites things it cuts things it chews things it pulverizes things it grinds things it grinds it turns yellow it is decayed it becomes blotched it becomes dark it is treated with dry color it rots it breaks it wiggles it moves it falls I pick my teeth I clean my teeth I wash my teeth I darken my teeth I break my teeth."

The twelfth and final book details the destruction of the empire and the cruelty of the Spaniards who annihilated warriors and raped a bunch of women during a festival when they were unarmed and unprepared, leaving guts everywhere. This was followed by a lengthy war, during which the Aztec people put up a good fight despite the numbers and technology against them. Spain had allied with the long-term enemies of the Aztec with the goal of erasing their empire and building a new Spain with the natives as slaves. This book was the only one that was mostly sympathetic to the Aztecs, and with the right crew I could see it being adapted into a great movie.

Flawed, biased, and incomplete as it may be, the Florentine Codex is probably the best and most comprehensive primary source on Aztec life, and anyone who wants to learn about Aztec culture and knows how to critically read prejudiced writing should definitely give it a read. All twelve books are now available in full for free on the Getty website, complete with English translations and the original illustrations.