Maya Long Count

The Maya Long Count is a linear calendar that fixes dates by counting the days elapsed since a fixed mythic starting point, rather than by locating them within a repeating cycle. It builds its units in a mostly base-twenty scheme: twenty days make a winal, eighteen winals a tun of 360 days, twenty tuns a katun, and twenty katuns a baktun of 144,000 days. A date names the tally of each unit since the creation date the inscriptions give as 4 Ajaw 8 Kumku, which the standard correlation places in 3114 BCE. The Long Count let the Classic Maya record events across many centuries with precision, and its thirteen-baktun cycle, completed in 2012, drew wide modern attention. These are the features of the Maya calendar tradition, carved on the monuments of the Classic period to anchor the deeds of the Maya lords in an unbroken count of days.

The standard correlation used to convert Long Count dates into the Gregorian calendar is the GMT correlation, named for Joseph Goodman, Juan Martinez Hernandez and J. Eric S. Thompson, which sets the creation date 0.0.0.0.0, 4 Ajaw 8 Kumk'u, at Julian day number 584,283, placing it at 11 or 13 August 3114 BCE depending on whether the proleptic Julian or Gregorian calendar is used for the conversion. It is not the only correlation ever proposed; the Spinden correlation, favoured by some earlier twentieth-century archaeologists, sets the same starting point about 260 years earlier, and the discrepancy between the two was for decades a live dispute, resolved in the GMT correlation's favour chiefly through radiocarbon dating of lintels at Tikal in the 1960s.

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.