After Columbus found the New World, hordes of Spanish colonists settled in the West Indies. Many of the colonists were ex-soldiers no longer able to find work in Europe. They eagerly left to stake a claim in the Indies for Spain. Bored by the day to day administrations of the colonies, they became restless. They traveled westwards again, toward the new frontier. The age the Spanish Conquistadores began.
The Aztecs were their most imposing foes. The Aztecs considered themselves chosen people of the gods. Their chief god was Huitzilpochtli (the Hummingbird Wizard) who represented the sun, the warrior, and fought the Aztecs' battles with the other gods to ensure the Aztecs' survival.
Huitzilpochtli needed food to nourish him so he could continue to fight. His preferred food was human blood.
In order to keep feeding Huitzilpochtli, the Aztecs warred continuously. Their army was of the utmost importance, and they had several different factions of warriors. The Knights of the Eagle and the Knights of the Jaguar were two such bodies of troops. These were the men who went forth to capture suitable human sacrifices.
Sacrifices were taken to the tops of the Aztec pyramids and laid upon a flat stone. There, their chests were cut open and their hearts were ripped out. The bodies were then thrown down the steps of the pyramid. The Spaniards who witnessed this violence were horrified.
More than blood lust prompted these ritual sacrifices. The Aztecs believed in a concept of "tonalli" or the "animating spirit". Tonalli was believed to be carried in the blood, and since blood flowed from the heart, this was the organ that was offered up to sate the god's appetite. It was believed that without these sacrifices, all motion would stop including the movement of the sun. The Aztecs' human sacrifices were intended to keep the sun from halting its orbit.
Also, the Aztecs did not have livestock. They practiced cannibalism on their captives. After the sacrifices tumbled down the stairs, the Aztec priests removed the limbs and cooked them. The hands and thighs were delicacies.
Estimates suggest 20,000 people a year were sacrificed by the Aztec royalty. This royalty was made up of a priest class. The priests directly served the Chosen Speaker. In Tenochtitlan, the Aztec capital city (with between 150,000 and 300,00 inhabitants it was one of the biggest metropolises in the world at the time) there were five thousand priests.
The priests painted their bodies black in order to symbolize religion and war. Their hair was matted with blood from human sacrifices. They filed their teeth to sharp points.
The Aztecs never fully conquered the surrounding states because they needed a continual supply of sacrifices for Huitzilpochtli. When the Spaniards came to conquer the Aztecs, they found numerous local allies. Even so, the Aztecs were not easily defeated, and much of their legacy is remembered.