The Egyptians, whose agriculture depended heavily on the annual overflowing of the Nile, initially used a lunar calendar. When they observed that the brightest star in the sky, Sirius, rose next to the sun every 365 days (about when the annual flooding of the Nile started) they devised a 365-day calendar that seems to have begun in 4236 B.C., the earliest recorded year in history.

The sun god, Aten was the most important of all the deities and his names and attributes varied greatly according to the time of day. The rising sun was named Khepri, the great scarab beetle and as the sun climbed toward mid-day it was called Ra, great and strong. When the sun set in the west it was known as Atum the old man, or Horus on the horizon. The god was not depicted in human form, but as rays of light extending from the sun's disk, as this solar-disk he was known as Aten.