Many of us would be lost without a calendar to help us remember dental appointments and important meetings, but in ancient Egypt, a calendar could mean the difference between feast and famine. Without a calendar, ancient Egyptians had no way of knowing when the annual flooding of the Nile would begin. Without that knowledge, their entire agricultural system would be put at risk, so a few thousand years before the common era, they started using one.
Their civil calendar was so closely tied into farming that the Egyptians divided it up into three main seasons: inundation, growing and harvest. Each season had four months, with each month divided into 30 days. Adding it all up, you get 360 days a year -- a bit short of an actual year. To make up the difference, the Egyptians added five days between the harvest and inundation seasons. These five epagomenal days, were designated as religious holidays set aside to honor the children of the gods [source: Weininger].