The Long Count Among the World's Calendars

Most calendars are cyclical: they name a position within a repeating period, and a date is ambiguous unless some larger cycle or era is supplied. The Maya Long Count is not. It is a plain tally of elapsed days from a fixed origin, written positionally in five places, and it therefore names a day uniquely across any span whatever, which no other pre-Columbian American system does and few ancient systems anywhere do.

The comparison it invites is with the Julian day number used by modern astronomers, which is likewise a linear count of days from an arbitrary origin adopted precisely because cyclical calendars are useless for computing intervals. The Long Count does the same work for the same reason and does it with a positional notation that includes a sign for zero.

The single irregularity is at the third place, where eighteen units rather than twenty make a tun of 360 days, bringing that unit near the solar year. Above it the count returns to multiplying by twenty and does not break again. Because the count is linear, two dated monuments anywhere in the Maya area can be placed in order and the interval between them stated exactly, independently of any correlation with the European calendar.