The number of seconds in a minute — and minutes in an hour — comes from the base-60 numeral system of ancient Mesopotamia. Developed around 3100 B.C., the sexagesimal system, as it is known, has fallen out of favor but is still used (with slight adjustments) to measure time and angles.

Most modern societies use the base-10 system (also called decimal) of Hindu-Arabic numerals. That system probably comes from counting on our two five-fingered hands, but because it has a limited number of divisors, 10 is actually an inefficient number on which to build a numeral system. Sixty, on the other hand, is eminently divisible — in mathematics, it is considered a “highly composite number” because it has more divisors than any smaller positive integer.

Georges Ifrah, a 20th-century French mathematician, proposed that the sexagesimal system grew out of an alternative method of counting known as the duodecimal system, common throughout Asia. Instead of counting the five digits on each hand, the thumb is used as a pointer, touching each of the four fingers on the right hand, beginning with the pinkie. When the count reaches 12, a digit on the left hand is lowered to mark the place — making “60” when all five digits are balled into a fist.

The Babylonians adopted the base-60 system from the Sumerians. In Babylonian astronomy, a year is 360 days, which is divided into 12 months of 30 days each. By 2000 B.C. the base-60 system had largely disappeared from common use, but it survives in our measures of months, days, hours, minutes and seconds, so called because they are the second division of 60 from the hour. Another vestige of Babylonian mathematics endures in the 360-degree circle.