Mexico City is the capital and largest city of Mexico. It is the most populous city in the Western Hemisphere and the second most populous city in the world. It is also one of the polluted cities in the world. The Aztec people were here before the Spanish came and founded Mexico City. It was refounded in 1521 by Hernán Cortés. Today, about 8.5 million people live in the city, and about 18 million live in the Greater Mexico City urban area. The city of Mexico City ceased to exist in 1928. Since then, there is only the Federal District.