Aztec city-states were independent, self-governing urban centers that formed the basis of the Aztec Empire in Mesoamerica, primarily from the 14th to the early 16th centuries. These city-states, known as 'altepetl,' were characterized by their own political systems, economies, and religious practices, while also being part of a larger network of tribute and trade relationships with one another. The most notable city-state was Tenochtitlan, which served as the capital and a hub of political and cultural life.