Aztecs were the people who lived in around the modern day Mexican territory. They are also known as the Pre-Columbian Mesoamerican civilization. The calendar that was used by this ancient civilization is known as the Aztec calendar. This particular calendar system was also adopted by the other Pre-Columbian civilization that settled around the central region of Mexico. The Aztec calendar is the most important calendars invented by the Pre-Columbian civilization and it is one of the few calendars that has a resemblance to the modern day calendar among all the other calendars that were used by the other civilizations in the Mesoamerican zone.
A typical Aztec calendar consisted of Xiuhpohualli and Tonalpohualli in its cycle. Xiuhpohualli was the name given to the year count and it consisted of 365 numbers of days in the calendar cycle. The day count was denoted by Tonalpohualli that consisted of a 260 days ritual cycle. Both the cycles together formed the "Calendar Round", which created a 52 year century. It was known that the very first calendric year aroused with the appearance of the Pleiades asterism in the east that occurred right before the first sunlight of the day broke in.
Tonolpohualli was the name of the day count in the Aztec calendars. It consisted of a total number of 260 days where each day was denoted by one of the 20 day signs along with a number from 1 to 13. There were day signs named after animals and environment which include names such as crocodile, wind, lizard, deer, rabbit, dog, serpent snake, alligator, jaguar, death, flower, monkey, house, reed, grass, eagle, vulture, earthquake, flint knife and rain. After the 13 count the calendar would restart counting with the number 1 again until it is 7 so that number 20 is made matching with all the 20 day signs to make one full cycle of 260 days.