How did our calendar come to be? Why do the seasons change? How did the days of the week get their names? And why is the year divided into days, weeks and months? From the Babylon of the moon-gazers to the Egypt of Eratosthenes and Ptolemy, through the Rome of the Caesars to the sixteenth-century Europe of Pope Gregory XIII, this is the awe-inspiring history of the measurement of time, presented in a fresh new way via the latest techniques in computer animation.