The Aztec underworld had 9 levels. These regions formed the layered realm called Mictlan, which many of the dead had to cross after dying from ordinary causes.
Aztec cosmology pictured the universe as vertically organized, with earthly existence between upper heavens and the underworld below. The underworld’s nine regions were not necessarily equivalent to nine levels of moral punishment. Instead, the dead encountered a sequence of supernatural obstacles on a difficult journey toward their final destination.
Mythic descriptions include mountains that crash together, fierce winds capable of stripping flesh, and dangerous rivers inhabited by threatening creatures. The journey was traditionally said to take four years, with Xolotl helping the dead navigate the passage. Mictlantecuhtli and Mictecacihuatl presided over the realm.
The number 9 is often confused with 13, but the two numbers refer to different parts of Aztec cosmology: the underworld had nine levels, while the heavens were commonly described as thirteen. Not everyone went to the underworld; the manner of death could determine another afterlife, including Tlalocan or a solar destination.