The two Mesoamerican cultures that relied upon the use of a calendar system were the?

The two Mesoamerican cultures that relied heavily on calendar systems were the Maya and the Aztec civilizations. The Maya developed a complex calendar system that included the Tzolk'in (a 260-day ritual calendar) and the Haab' (a 365-day solar calendar), which were used for agricultural, religious, and ceremonial purposes. The Aztecs also had a similar system, utilizing the Tonalpohualli (a 260-day calendar) alongside the Xiuhpohualli (a 365-day calendar), integrating these calendars into their societal and religious practices. Both cultures demonstrated remarkable astronomical knowledge through their calendar systems.