The solar calendar of 365 days, called 'Xiuhpohualli', the Vague Year, was composed of 18 'months' of 20 days each, called veintenas, divided into four five-day weeks. A period of 5 days was added at the end. The 360-day period was called 'Xihuitl' by Aztecs, and 'Haab' or 'Tun' by the Maya.he Aztec Calendar Stone is a symbolic portrayal of the four disasters that led to the demise of the four prior Universes in Aztec cosmology. It also contains a hieroglyphic and pictographic layout of how the Aztecs measured time. The stone has both mythological and astronomical significance.