<human>:  What are some interesting facts about the history of the Aztec civilization?
<bot>: 
1. The Aztec civilization flourished in Central Mexico from the 14th to 16th centuries.
2. The Aztecs built one of the most advanced societies in Mesoamerica and their capital was the sophisticated city of Tenochtitlan.
3. The Aztecs believed their gods required human sacrifices at certain times.
4. The Aztecs developed a complex irrigation system, an astronomical calendar and a form of hieroglyphic writing.
5. Their economy was based on tribute paid by conquered tribes, which were also used as slave labor for large public works, for example, constructing the city of Tenochtitlán.
6. The Aztecs had a system of government that included an emperor, nobility and a priestly class.
7. The Aztec empire was conquered by the Spanish in 
1521.