About a thousand years ago, according to legend, the Aztec people started walking from North America southwards, searching for a special place to settle and build a city. After years of travelling they came to a swamp, and on an island in the middle of it they saw the special sign they had been looking for - an eagle on a cactus eating a snake. Today the lake is covered by Mexico City, one of the biggest cities in the world, and the sign of the eagle eating a snake is in the middle of the Mexican flag.
