The Egyptian year
One of ancient Egypt's most important legacies is the lunar calendar comprising 365 days. In use as early as 2800 B.C., it comprised 12 months of 30 days each, with five additional days known as the "five days beyond the year". The months were divided into three "weeks" of 10 days each, while the year was divided into three seasons of four months each: Akhet (Flood Season), Peret (Growth Season) and Shemu (Dry Season).

The new year was established by the heliacal rising of Sirius (Alpha Canis Majoris: Sopde t in Egyptian, whence Sothis in Greek, literally "the pointed one" probably a reference to its intense brightness). Sirius reappears at sunrise on or around 19 July. This event was seen as bearing a direct causal relationship to the simultaneous start of the Nile's annual flooding.

The ancient Egyptians gave their months numbers rather than names; nor was there a given "start date" from which all subsequent years could be counted. Each reign began with the year 1, for example: "Year 19 of the reign, 4th month of Peret, day 14."

In the most ancient times, dating tended to refer to the cattle count that took place every two years, for instance "the year after the 18th cattle count" coincided with the 37th year of the reign.