The Aztec and Maya are renowned for their sophisticed system of mathematics based upon the number 20. It should not be a surprise to learn that the ancient Tiwanakotas, the people of Tiwanaku , Bolivia, also counted in twenties... Not only did they divide the year by 20 to obtain a fortnight of 18 days, they also divided a minute of latitude of their city by 60 x 60 (3600) to arrive at a cubit of 20 inches. The freize of the Gate of the Sun, whose icons represent the workings of the Calendar, is 100 inches wide, that is, five cubits of 20 inches, or 10 decimal feet of 10 inches. The year similarly could be considered 20 fortnights of 18 days or 10 months of 36 days.

The calendar is not the Gate of the Sun, but the wall, originally of 11 pillars behind the Gate of the Sun where the sun would set every evening. Located in the oldest part of Tiwanaku, the question is really whether there was an even older culture, perhaps an earlier city underground beneath Tiwanaku, or under the nearby lake, or was this science originated an at earlier Atlantis site such as Pampa Aullagas and subsequently destroyed by earthquakes and floods so no trace remains? Tiwanaku itself was abandoned and in ruins at the time of the Conquest, but even then, the first chronicler to visit it, Ponce de Leon, reported that the Aymara year was divided into 10, not at all like the Inca calendar which was later revised into 12 months.

Animation of 1 year of the Tiwanaku calendar, counting 40 weeks of 9 days, 20 half-months of 18 days, 10 months of 36 days: sidereal lunar months, zocam years of 20 sidereal months, acrotom years of 40 sidereal months or 3 solar years, the Saros cycles of 18 solar years = 20 Inca years of 12 sidereal months.