What is the capital of Mexico?

Mexico City stands on the site of Tenochtitlan, the Mexica capital built on islands in a lake in the Valley of Mexico and reached by causeways. After the Spanish conquest, Hernán Cortés deliberately rebuilt the colonial capital on the same spot rather than founding a new one elsewhere, laying the cathedral and the viceregal palace over the ceremonial precinct as a statement of succession. That decision created the city's defining engineering problem. The Spanish drained the lakes to stop flooding, and the soft lakebed clay beneath has been compacting ever since, especially as groundwater is pumped out, so buildings tilt and sink at different rates and the historic centre visibly leans. The same basin traps air at high altitude, which is why pollution was so persistent, and the valley sits in a seismically active region where the old lake sediments amplify earthquake shaking dramatically.

Excavation beside the cathedral uncovered the Templo Mayor, the main Mexica temple, buried directly beneath the colonial centre.