This article argues that calendars are distinctive signifiers of cultural identity. People are distinguished by how they measure time. From their birthday onwards their scheme of time places them in precise relationships with their society, their secular ruler and their concept of cosmic order Complications arise with the co-existence of time systems, lunar and solar calendars. The collision and interpenetration of cultures is reflected in their time systems. Major eras have political, historical or religious origins, but the Byzantine Year of the World (Annus Mundi) has an inbuilt end of time at the Eighth Day, Millennium or Era, precisely from 7001 AM or 1492 ad, when, instead of the end of the world, came the unexpected discovery of a new world.