Dating work along the Nile
Life along the Nile involved seasonal farming, transport and supplies. Royal institutions and temples recorded grain, work obligations and ceremonies using dates. A civil calendar was already part of administration during the Old Kingdom. Documents commonly counted years within a ruler’s reign and specified a month and day. A new reign restarted the year count, so records identified both the authority under which an activity took place and its position in time.
Twelve months and five additional days
The civil year contained twelve months of thirty days, followed by five additional days. Four months formed each of three seasons associated with inundation, growth and harvest. Regular month lengths made the sequence useful for accounts and scheduled supplies. The additional days stood outside the ordinary months and had religious associations. Egyptian communities also used lunar reckoning for religious purposes, allowing different calendars to operate alongside one another within the same society.
A fixed year beside changing seasonal dates
A 365-day year is slightly shorter than the cycle of the seasons. Without regular leap days, civil dates gradually moved through the seasonal year. Observations of Sirius, the river and other natural changes continued to provide practical information. The later Alexandrian calendar added a periodic extra day. Related structures survive in Coptic and Ethiopian calendars, with twelve thirty-day months followed by a short final month.