The Aztec Empire: How Tenochtitlan's Builders Engineered a Lake City

The Aztec civilization, built primarily by the Mexica people, flourished in central Mexico from roughly 1345 to 1521 CE, according to the World History Encyclopedia. Its capital, Tenochtitlan, grew from a marshy island in Lake Texcoco into one of the largest cities in the pre-Columbian Americas, before it was conquered by Spanish forces under Hernán Cortés in 1521.

Origins and the founding of Tenochtitlan

According to the World History Encyclopedia, the Mexica migrated from a mythical homeland called Aztlán in northwest Mesoamerica and settled in the Valley of Mexico around 1100 CE. Tradition holds that their god Huitzilopochtli told them to build their city where they saw an eagle perched on a cactus eating a snake; they identified this sign on an island in Lake Texcoco and founded Tenochtitlan there around 1325 CE, as described by National Geographic Education.

For its first century, Tenochtitlan was a minor city-state subordinate to the Tepanec people. That changed after the Tepanec War of 1428, when Tenochtitlan joined with the city-states of Texcoco and Tlacopan to form the Triple Alliance, according to the World History Encyclopedia. This coalition launched the territorial expansion that produced the Aztec Empire, with Tenochtitlan's ruler eventually holding the title huey tlatoque, or "high king," over the alliance.

Empire, society and daily tribute

By the early 16th century, the empire the Triple Alliance built covered an estimated 135,000 square kilometers and governed roughly 11 million people, per the World History Encyclopedia. Conquered city-states were not directly administered but required to pay regular tribute in goods, labor and, in some cases, captives for ritual purposes, while the empire relied on strategic marriages, gift-giving, monumental art and the threat of military force to hold its territory together.

Aztec society was organized into defined classes: local rulers (teteuhctin), nobles (pipiltin), commoners (macehualtin), serfs (mayeque) and slaves (tlacohtin), with some mobility possible among the lower ranks, the World History Encyclopedia reports. All adult men were expected to serve in the military, and elite warrior orders such as the Eagle and Jaguar warriors fought with cotton armor and obsidian-edged clubs called macuahuitl.

Urban planning on a lake

Tenochtitlan was built on islands in Lake Texcoco and eventually covered more than 13 square kilometers, with a symmetrical layout of four main sectors divided by causeways and canals radiating from a central ceremonial precinct, according to National Geographic Education. National Geographic Education and the World History Encyclopedia both cite a population of roughly 200,000 residents by the early 1500s, with the World History Encyclopedia describing Tenochtitlan as the largest city in the pre-Columbian Americas at that time.

To expand usable land on the lake, the Aztecs built chinampas — raised, artificial agricultural plots constructed above the waterline and anchored with vegetation and silt — which National Geographic Education credits with sustainably feeding the growing capital. Multiple causeways doubled as dikes, connecting the island to the mainland while separating freshwater from the lake's salt water, according to the same source.

The Templo Mayor

At the heart of the city stood the Templo Mayor, a dual pyramid with twin shrines dedicated to Huitzilopochtli, the god of war and the sun, and Tlaloc, the god of rain, according to both National Geographic Education and the World History Encyclopedia. The structure was rebuilt and enlarged in multiple stages, reflecting successive rulers' efforts to expand and reconsecrate the site.

Much of what is known about the temple's layered construction comes from archaeology rather than colonial-era texts alone. In 1978, excavation work near the Templo Mayor site in downtown Mexico City uncovered a buried, carved stone disc, as reported by Mexico News Daily. The find, known as the Coyolxauhqui Stone and dated to around 1473 during the reign of Axayacatl, depicts the dismemberment of the moon goddess Coyolxauhqui by her brother Huitzilopochtli and was found at the foot of the temple, according to the same source.

The discovery, led by archaeologist Eduardo Matos Moctezuma, prompted a sustained excavation of the site beneath Mexico City's historic center, according to Mexico News Daily. Subsequent digs there have uncovered further offerings, including the skeletal remains of a child dressed in Huitzilopochtli's regalia, found in 2005.

Religion, calendars and the fall of the empire

Aztec religious life combined two calendar systems: a 260-day ritual calendar used for divination and a 365-day solar calendar, National Geographic Education reports. Religious ceremonies at sites such as the Templo Mayor included music, incense, bloodletting and both animal and human sacrifice, practices the World History Encyclopedia says were tied to beliefs about sustaining the sun and cosmic balance; the empire also fought so-called Flowery Wars specifically to take captives for sacrifice.

The empire's end came rapidly after Spanish conquistador Hernán Cortés arrived on the Mexican coast and marched to Tenochtitlan in 1519. Cortés initially took the Aztec ruler Moctezuma II hostage, but relations collapsed, and Spanish forces were driven from the city on June 30, 1520, during an episode remembered as the Noche Triste, according to the World History Encyclopedia. Cortés regrouped with the help of Tlaxcala and other peoples who resented Aztec tribute demands, and after a 93-day siege, Tenochtitlan fell on August 13, 1521, when the Aztec leader Cuauhtemoc surrendered.

The World History Encyclopedia lists smallpox, superior Spanish weaponry and the defection of rival Mesoamerican peoples among the key factors in the empire's collapse. Cortés subsequently built colonial Mexico City over the ruins of Tenochtitlan, and the lake that once surrounded the Aztec capital was gradually drained in the following centuries.