Mexico City is the capital and largest city in Mexico. One of the most important political, cultural, educational, and financial centers in North America. Founded in 1521, it is also one of the most populous and polluted cities in the world. Today, about 8.5 million people live in the city, and about 18 million live in the Greater Mexico City urban area. It has the second highest number of people in the world after Tokyo in Japan. The Aztec people were here before the Spanish came and established Mexico City. The City ceased to exist in 1928. Since then, there is only the Federal District.