Can someone tell me what an Aztec codex is? I assumed Aztec writing was not on paper but on stone... these seem to be from the colonial period, so are they hybrid cultural forms or what?
It's a book. Paper bark or parchment. . The Aztecs didn't have full writing in the sense of a system to represent a spoken language. Aztec codices are more to the calendar and graphic end of things. (But I could be wrong, since so few examples, are truly from pre-exchange times.)
The primacy of stone is a misconception. The following applies not just to the Aztecs, but also Sumer and Babylon, Egypt, the Maya, etc: the primary writing material for all of these civilizations was not stone. It was perishable materials, including parchment, wood bark, wax tablets, papyrus in Egypt, or just drawing in a pile of fine sand to do some arithmetic. (Babylon and its fired clay is a bit of an exception, maybe. But they also wrote on wood, bark paper and cloth, among other things.)
That means we only get monumental inscriptions. I'm more familiar with the Maya, who did have a complete writing system for spoken language, and we strongly suspect the Maya had literature in the same way the Egyptians, Chinese or Sumerians did. Poetry anthologies, mythological anthologies, religious texts, and also textbooks on medicine and astronomy, etc. Obviously, they didn't carve those on monuments, they wrote them on the closest analogue to paper they had.
Unfortunately, neither Mexico's meteorological climate nor Spain's religious climate at the time was conducive to preserving such fragile books.
> Babylon and its fired clay is a bit of an exception
It wasn’t just Babylon but dozens of other civilizations in the region. IIRC we have a lot more Assyrian tablets because Babylon and their allies sacked and burned the Assyrian capital which preserved their library.
They had a pre-colombian pictographic writing system with some phonetic elements that they wrote on animal hides. Priests did most of the writing and there was quite a lot recorded by them before it was mostly destroyed after contact with Europe.
Codex means a book in the modern sense of bound leaves one can flip through for random access to any one page. The opposite is volume or scroll, which involves sequential reading or scrolling to arrive at a particular page (like tape storage).
