The Aztecs were a Pre-Columbian Mesoamerican people who originated as nomadic tribes called the Mexicas. According to prophecy, they traveled until finding an eagle on a cactus as a sign to build their city of Tenochtitlan, which later became Mexico City. Religion played a central role in Aztec society, with temples dedicated to gods and human sacrifice seen as necessary to please the gods and ensure prosperity. At its height, the Aztec Empire spanned Mesoamerica through military conquest but fell after the arrival of the Spanish in 1519 due to war, disease, and alliances with resentful conquered peoples.