They built a capital in the middle of a lake
TENOCHTITLAN was founded on a swampy island in Lake Texcoco, which is an absurd place to put a city, and the Aztecs made it work with engineering. Three broad causeways connected it to the shore, each with removable wooden bridges for defence. An aqueduct brought drinking water from springs at Chapultepec. A ten-mile dyke held back the brackish eastern water to keep the western side fresh.
Farmland was manufactured. Chinampas — rectangular plots built up from lake mud and staked with willows whose roots anchored them — produced several harvests a year and could be reached by CANOE. By 1500 the city held perhaps 200,000 people, making it larger than any city in Europe at the time except possibly Constantinople. Mexico City now sits on top of it, sinking slowly into the drained lake bed.
The market astonished the people who destroyed it
The Spanish soldier Bernal Díaz, writing decades later, described the MARKET at Tlatelolco as bigger than anything in Rome or Constantinople, with 60,000 people trading on a busy day and everything sorted into sections — one street for pottery, another for feathers, another for dogs. Judges sat in the square to settle disputes on the spot.
COCOA beans were the small change. A rabbit cost around thirty; a canoe, rather more. Because the beans were currency there was counterfeiting, with hollowed-out shells packed with mud, and the Spanish crown kept using them as coinage for decades afterwards because the system worked. Anyone with an obsidian blade, a load of MAIZE or a stack of cotton cloth could turn up and trade.
The sacrifices were real and the numbers are contested
Human SACRIFICE was central to Aztec state religion and is not in doubt — the Templo Mayor excavations have produced skull racks with thousands of individuals. It was a public, official act tied to keeping the SUN moving, and the victims were mostly war captives.
The figures reported by the conquistadors are the disputed part. Claims of 80,000 killed at a single temple dedication are now generally treated as propaganda by people who needed to justify a conquest, and archaeological counts come out very much lower. Both things are true at once: a society that did this, and a set of sources with an obvious interest in exaggerating it. Our Aztec mythology page covers the beliefs behind it.
What else is in the grid
OBSIDIAN — volcanic glass, flaked to an edge sharper than steel and set into wooden clubs, which is what the Aztec WARRIOR actually fought with, since the region had no iron. FEATHERS from tropical birds were worked into mosaics and cloaks by specialist craftsmen and valued above GOLD, which the Aztecs regarded as decorative rather than precious.
Also the EAGLE and the JAGUAR, the two elite warrior orders; the CODEX, painted on bark paper and folded like a screen, of which a handful survive out of thousands burned; the CALENDAR system running two interlocking cycles at once; the stepped PYRAMID and the TEMPLE on top; the feathered SERPENT; and the EMPEROR, whose title Moctezuma held over a tribute EMPIRE rather than a unified state — which is how a few hundred Spaniards found so many local allies willing to help bring it down.