Historically, there is no aspect of the Aztec culture that shocks us more than human sacrifice. As hard as it is for us to imagine it, imagine how the first conquistadors felt when they witnessed it for the first time. It left them completely horrified, and then some of their own men met the same fate. To their horror, they would discover their fellow Spaniards grinning heads displayed on a tzompantli (a horizontal pole).
The Aztec citizens first duty was to provide nourishment for the mother and father, the earth and sun. They believed to keep the sun on its course, and prevent darkness from over-taking the world forever, it was necessary everyday to feed it its precious “chalchiuatl” or human blood. Without blood the world would stop. Each time a priest stood on top of a pyramid and held up a bleeding heart and placed it in the “quauhxixalli” (where the hearts were burned with copal incense), a disaster was thwarted and the end of the world was postponed once more. The Aztec's believed that life was made out of death.
The sacrifice of humans was not inspired by cruelty or hatred. Instead it was their response to a constantly threatening world. The victim was not thought of as an enemy, but as a messenger to the gods. The warrior who had taken the victim captive knew that one day he too would face the same destiny.
Human sacrifice was believed to have been introduced to the Aztecs by the Toltecs. It was performed almost exactly the same way by the Mayans. First, conch horns sounded and the victim was led to the top of the pyramid. Four priests held the victim still as he laid stretched out on his back on a flat or convex stone. A fifth priest dressed in a black robe with long black hair cut out the heart with a flint or obsidian knife. Occasionally, victims were allowed to fight for freedom, and if he defeated several Aztec warriors he was allowed to live. Sadly, this almost never happened. These special warriors wore their own unique costumes and they were well respected.
This was not the only type of sacrifice. Women were sacrificed during dances, children were sacrificed to the rain god Tlaloc, and victims were burned in fires in honor of the fire god. Also, like the Mayans, the Aztecs would dress their victims up to look like their god of choice, attach him to a wooden frame and shoot him full of arrows. When the Aztecs practiced cannibalism after the rites they believed that they were eating god's own flesh.