The ancient Maya created several interlocking calendar systems. The Sacred Round of 260 days is the longest lasting, since it is still in use in some places today. In former times, it was often combined with another system, a 365-day Vague Year, to create a cycle called the Calendar Round, in which a date would repeat once in every 52 years.
Another system, called the Long Count, was used to record longer spans of time. It tracked the passing days from a single starting point many trillions of years in the past. If we look at a single Maya date written with all three systems, a Sacred Round, a Vague Year, and Long Count, we have a time-reckoning that is not unlike our own days, weeks, months, years, decades, and millennia.