Mexico City’s mix of cultures is the legacy of its history.

In the 16th century, after the conquest of the Aztec empire by Hernan Cortez, the Spaniards built a European city on the site of the Aztec capital, Tenochtitlan.

Today, Mexico City is one of the world’s largest cities, with a population of more than 20 million in the metropolitan area.

It is also one of the most polluted, because the mountains that surround the city trap industrial and automobile pollution.

The city was built on an island in an ancient lake and, as a result, buildings are sinking noticeably as underground water is drawn for the use of the city’s huge population.