Mesoamerican Long Count calendar

The Mesoamerican Long Count calendar is a non-repeating base-20 and base-18 calendar used by several pre-Columbian Mesoamerican cultures, most notably the Maya. For this reason, it is often known as the Maya Long Count calendar. Using a modified vigesimal tally, the Long Count calendar identifies a day by counting the number of days passed since a mythical creation date that corresponds to August 11, 3114 BCE in the proleptic Gregorian calendar. The Long Count calendar was widely used on monuments. The two most widely used calendars in pre-Columbian Mesoamerica were the 260-day Tzolkʼin and the 365-day Haabʼ. The equivalent Aztec calendars are known in Nahuatl as the Tonalpohualli and Xiuhpohualli, respectively. The combination of a Haabʼ and a Tzolkʼin date identifies a day in a combination which does not occur again for 18,980 days (52 Haabʼ cycles of 365 days equals 73 Tzolkʼin cycles of 260 days, approximately 52 years), a period known as the Calendar Round. To identify days over periods longer than this, Mesoamericans used the Long Count calendar. The Long Count calendar identifies a date by counting the number of days from a starting date that is generally calculated to be August 11, 3114 BCE in the proleptic Gregorian calendar or September 6 in the Julian calendar (or −3113 in astronomical year numbering). There has been much debate over the precise correlation between the Western calendars and the Long Count calendars. The August 11 date is based on the GMT correlation. The completion of 13 bʼakʼtuns (August 11, 3114 BCE) marks the Creation of the world of human beings according to the Maya. On this day, Raised-up-Sky-Lord caused three stones to be set by associated gods at Lying-Down-Sky, First-Three-Stone-Place. Because the sky still lay on the primordial sea, it was black. The setting of the three stones centered the cosmos which allowed the sky to be raised, revealing the sun. Rather than using a base 10 scheme, the Long Count days were tallied in a modified base-20 scheme. In a pure base 20 scheme, 0.