Almost everything strange about Mexico City follows from one fact: it is built on a lake that is no longer there.
Tenochtitlan
The Mexica arrived in the Valley of Mexico late, and were pushed onto an unpromising island in Lake Texcoco. According to their own account, they had been told to settle where they saw an eagle on a cactus eating a serpent — the image now on the flag — and they saw it there in 1325.
What they built on that island was, by 1500, one of the largest cities in the world: perhaps 200,000 people, larger than any city in Europe except possibly Constantinople.
It worked because of engineering. Causeways connected the island to the shore, with removable bridges. An aqueduct from Chapultepec brought fresh water. A ten-mile dyke, built under Nezahualcóyotl, separated the brackish eastern lake from the fresh western part and controlled flooding. Chinampas — artificial garden plots built up from lake mud — fed the city with several harvests a year.
Cortés’s soldiers, arriving in 1519, compared it to Venice and to the enchantments in the romances they had read. Bernal Díaz wrote that some of them asked whether what they saw was a dream.
1521
Cortés arrived with a few hundred men and left with tens of thousands of indigenous allies — principally the Tlaxcalans, who had been at war with the Mexica for generations. That, and smallpox, which reached the city in 1520 and killed a very large share of the population including the emperor Cuitláhuac, is what brought Tenochtitlan down.
The siege lasted from May to August 1521. Cortés cut the aqueduct and the causeways and took the city street by street, demolishing buildings as he advanced.
Cuauhtémoc, the last emperor, was captured at Tlatelolco on 13 August.
The Spanish then built their capital on exactly the same spot, using the same stone. The cathedral stands beside the Templo Mayor; the National Palace stands on Moctezuma’s.
The draining
An island city works if you maintain the hydraulic system. The Spanish did not.
The dyke was neglected and the lake flooded the city repeatedly — the flood of 1629 lasted five years and killed thousands, and the authorities seriously considered abandoning the site.
The response was to drain the lake, beginning with the Nochistongo cut in 1607 and continuing for over three centuries: the Gran Canal in 1900, the Emisor Poniente, the deep drainage tunnels of the 1970s, and the Túnel Emisor Oriente completed in 2019.
It is one of the longest continuous engineering projects in human history and it has essentially succeeded. Lake Texcoco is gone.
The consequences
The city is sinking. With the lake drained and groundwater pumped out from beneath — the city still draws most of its water from the aquifer — the clay compacts. Parts of the historic centre have dropped more than ten metres since the conquest, and some outer districts sink up to 40 centimetres a year.
You can see it. The cathedral floor slopes. Bellas Artes has sunk four metres and you walk down into a building designed to be entered up steps. The old basilica at Guadalupe tilts visibly.
The ground amplifies earthquakes. Soft saturated clay does not damp seismic waves, it magnifies them and can resonate for minutes. That is why a quake centred hundreds of kilometres away on the Pacific coast destroys buildings here — 1985 and 2017 both.
And the city floods and runs short of water at the same time. Rain runs off the paved valley with nowhere to soak, while the aquifer is overdrawn and some districts receive water only intermittently by tanker.
Every one of those problems is the lake, still being dealt with five centuries later.
Where to see it
Templo Mayor — the temple itself, several metres below the modern street.
Xochimilco — the surviving canals and chinampas, and the only place the lake system is still working.
Plaza de las Tres Culturas — Tlatelolco’s ruins, the colonial church built from them, and a 1960s tower block, in one view.
The Zócalo itself, which is the ceremonial precinct of Tenochtitlan with a different city on top of it.
The water problem now
The consequence that matters most today is not the sinking but the supply.
Mexico City draws a large share of its water from the aquifer beneath it, faster than it recharges — which is what causes the subsidence. The rest is pumped uphill from the Cutzamala system, over a thousand metres of lift, at enormous energy cost.
Meanwhile roughly 40 per cent is lost to leaks in pipes broken by the very subsidence the pumping causes, and rain runs off the paved valley into the drainage tunnels and out of the basin entirely.
In 2024 the Cutzamala reservoirs fell to historic lows and there was serious public discussion of a Day Zero. Several boroughs receive water only on a schedule, delivered by tanker.
A city built on a lake now has to import its water. That is the whole story in one sentence.
Reading
Jonathan Kandell’s La Capital is the standard popular history. Fernando Cervantes’ Conquistadores is the recent reassessment of 1521. Camilla Townsend’s Fifth Sun tells the conquest from Nahua sources rather than Spanish ones, and is the one to read if you read only one.