The Aztecs believed that the sun died every night and was reborn every morning. They saw this as a cyclical process, with the sun god Tonatiuh sacrificing himself each evening to ensure the continuation of life.

Here's a breakdown of their beliefs:

* The Sun's Journey: They envisioned the sun as traveling across the sky each day, reaching its peak at midday. Then, as it descended in the west, it entered the underworld (Mictlan) and engaged in a fierce battle with the forces of darkness.

* The Sacrifice: Tonatiuh, being a powerful but ultimately mortal deity, needed nourishment to sustain his strength. The Aztecs believed this nourishment came from the blood of human sacrifices. They performed elaborate rituals, offering the hearts and blood of victims to appease the sun god and ensure his resurrection.

* The Rebirth: Tonatiuh, fueled by the blood sacrifice, would conquer the darkness and emerge from the east, heralding the dawn and bringing life back to the world.

This belief in the sun's daily death and rebirth was central to Aztec cosmology and influenced their rituals, art, and societal structures.