Stop 15 of 109 · Why Sixty?
c. 700 BCE · Babylon, Mesopotamia
Why Your Hour Has Sixty Minutes
Babylonian scribes counted in sixties rather than tens, and the habit outlived their entire civilization to land inside every clock made since.
By around 700 BCE, scribes in Babylon were doing arithmetic in a base-sixty, or sexagesimal, number system, rather than the base-ten system most of the world uses today. One popular explanation says the choice goes back to counting finger joints: a thumb ticking off twelve joints on one hand, five times over, reaches sixty. It is a charming idea, but there is no real evidence for it. A more sober theory points to trade, since Babylonian weights ran sixty shekels to a mina.
Whatever its origin, sixty has a genuine practical advantage over ten: it can be divided evenly by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20 and 30, which makes splitting a quantity into thirds or twelfths, sums that come up constantly in trade and measurement, far cleaner than they are in base ten.
That same base-sixty logic was applied to time. The Babylonian day held twelve double-hours, called bēru, and sky-watchers further divided the day into 360 smaller units of four minutes each, called UŠ.
At night, scribes tracked the hours with a water clock, measured by weight rather than depth, in units called mana: four mana of water for a long winter watch, three at the equinox, and only two in summer.
Classical Greece later borrowed Babylon's twelve-part division of the day, and from there the sexagesimal habit worked its way, unbroken, into the sixty minutes of an hour and the sixty seconds of a minute that every watch on Earth still keeps.