We take the measurement of time for granted, yet our lives are punctuated by dates: Christmas, Passover, New Year, Mother's Day, birthdays, pay-day. Some events are world-wide holidays, while others are celebrated by only a few. At what point in history did mankind begin to organize time? How did the patterns of the sun, moon and stars influence the way in which we mark our hours and day? When and how did we establish the cycles of time that make a season, a decade, a century or a millennium?