sentences:  Since their months were made of no more than twenty days, these were all the days contained in a month, because they were not guided by the moon but by the days; therefore, the year had eighteen months.The days of the year were counted twenty by twenty.The calendar, (in history known as the "vague year" which means no leap day) had its antecedents in form and function in earlier Mesoamerican calendars, and the 365-day count has a long history of use throughout the region.