The ancient Mayan Indians of Central America gave much importance to time and its passing. They had two calendars--the "sacred" calendar and the "true year" calendar. The latter had 365 days and was amazingly accurate ; it is even more precise than our modern calendar. The Mayans also set up monuments with obvious regularity to mark the passing of time--every twenty years in some cities, or every five years or ten years in other cities. This was done for more than 1500 years. To the Mayans the date was all important; nothing else seemed worthy of being marked on stones.