Not one calendar but a set of interlocking cycles — a 260-day ritual round, a 365-day solar year, and a linear day-count reaching back to a mythical creation — built on a base-20 place-value system and an independently developed sign for zero. It let Maya scribes fix any day in deep time, schedule the rituals of kingship, and write some of the most sophisticated astronomical tables of the pre-Columbian Americas.
On 21 December 2012, parts of the modern world braced for the end. The Maya calendar, the story went, had run out. It had not. What happened that day was that a single long count finished its thirteenth great cycle and rolled over to begin the next, the way an odometer turns from 99,999 to 100,000. The Maya never wrote an apocalypse. They wrote machinery for counting time so far in both directions that no human life could exhaust it.