The Aztecs were constantly at war, and warriors were so important to their culture that new rulers had to start their rule on the battle field, expanding the size of the empire, and capturing prisoners for ritual sacrifice to the gods. As a militaristic society, the Aztecs placed a very high emphasis on honor and battlefield skill: the ideal warrior was noble, brave and had to serve and respect the gods.

The Aztecs didn't maintain a standing army, but in such a militaristic society great numbers of warriors were required and every able-bodied man of a tribe was a soldier of sorts. All boys were taught fighting with a number of different weapons in the telpuchcalli (houses of youth) from the age of fifteen.

When the Spaniards arrived in Mexico they faced armies of elite Aztec warriors, and the most feared and famous of all Aztec soldiers were the fierce rival castes of the Eagle Knights of Huitzilopchtli and the Jaguar Knights of Tezcatlipoca. The Aztecs recognized the duality of the world between darkness and light, and the warrior orders symbolically reflected this conflict: the eagle was the greatest predator of the day, the jaguar was that of the night. There was also a third, not often mentioned, order, that of the Arrow. In battle, the Knights of the Eagle and Jaguar generally acted as military officers of sorts, in charge of brigades composed of the forces of two or more clans.

The Jaguar and Eagle Knights were distinguished by their distinctive uniform and helmets: the Jaguar warriors wore elaborately plumed headgear and Jaguar pelts with their faces peering out of the animals head, and the Eagle warriors wore feathered helmets with a gaping beak. Weaponry included the chimalli (war shield), the maquahuitl (club set with sharp obsidian blades), wooden spears with obsidian-edged blades, and flint and obsidian obsidian-tipped knives and swords.

Admission to the prestigious orders of Eagle or Jaguar warriors was reserved only for nobles and those who distinguished themselves in battle by capturing enemy soldiers. Each captive taken advanced a warrior along different orders, and the fourth allowed admission to the elite Jaguar Knights. This rank provided unique benefits and privileges, including exemption from taxation and tribute, taking part in war councils, taking concubines, invitations to dine in the royal palace, and participation in cannibalistic feasts.