Answer:When the Aztecs saw an eagle perched on a cactus on the marshy land near the southwest border of Lake Texcoco, they took it as a sign to build their settlement there.
The sign was to be an eagle perched on a cactus and eating a snake. According to the legend, they saw this sign on an island in a central Mexico lake. This island became the center of their empire. The symbol of the eagle, cactus, and snake appears on Mexico's flag today
