fincher.org: World History Timeline Citat: "...3114 BC, Aug 13...Start of the Mayan calendar. The Mayans had 20 days in their month starting with day 0 and ending with day 19. They understood zero not only as a place holder, but as a true counting number..."
shaw.ca: Note on the Maya Calendar Citat: "...Zero is usually indicated by a "shell" glyph...The long count is actually a modified base 20 number system: All periods except the tun are 20 times the previous period. The Maya used place holding arithmetic and the concept of zero before they were invented in the Old World..."
