The official practice of numbering the years in sequence started with the emperor Seleucus. He chose 311 B.C.E., the year he came to power, as the year One. The Seleucid system was adopted by the Jews of Babylon who referred to this newly accepted practice as the "era of dating legal documents". About 700 years later the Jews of Babylonia recalculated the number for the Jewish calendar and that is the dating system used today. Today, the majority of the world uses the Egyptian solar calendar. The following clips discuss the development of this new way of marking time. Other calculations such as the number of hours of the day, are a human invention. This podcast also explores the sophistication of astronomy and math in the ancient world and the reconciliation of the solar and lunar calendar systems.