Math & science · c. 2,800 BCE

365-day civil calendar

Egypt fixes a 365-day year of twelve 30-day months plus five extra days.

Tied to the Nile flood and the heliacal rising of Sirius, the Egyptian civil calendar was simple enough to run for millennia. It became the direct ancestor of the Julian and Gregorian calendars.

See it in the living tree Wikipedia

Arcs above join it to what it stood on, arcs below to what it led to. The bar places this stretch on the tree's whole timeline.

What it built on 2

Numerals and arithmetic 3000 BCE
Agriculture 9500 BCE

What it led to 2

Babylonian astronomy 700 BCE
Julian calendar 45 BCE