Here is something you never question until someone points at it. Almost everything you count runs in tens. Money, metres, the digits on your own hands. But time refuses to play along. Sixty seconds in a minute, sixty minutes in an hour, and then, oddly, twenty-four hours in a day. Nobody woke up one morning and chose this. You are reading time off a system built by a civilisation that had crumbled to dust two thousand years before the first mechanical clock ever ticked. The clock on your wall is a fossil.
01 · The culpritsA dead empire is running your watch
The trail runs back about four thousand years, to the flat river country of Mesopotamia: the Sumerians first, and then the Babylonians who took over their mathematics. These people did something almost no other culture did. They counted in base 60, a system called sexagesimal. Where we roll over to a new column every ten, they rolled over every sixty. It sounds baroque, even perverse. But it was a stroke of quiet genius, and we never stopped using it. Every time you say “half past” or “quarter to,” you are speaking fluent Babylonian.
02 · The reason for 60The most divisible number in town
So why 60, of all numbers? Because 60 is the smallest number you can cleanly divide by 1, 2, 3, 4, 5 and 6. Sit with how useful that is. You can split it in half, in thirds, in quarters, in fifths, in sixths, and every single time you get a whole number, no awkward remainder. Now remember these people had no decimal point, no neat “0.25” to lean on. They lived in a world of fractions, of thirds of a field and sixths of a shekel. A number that shattered so cleanly into so many pieces was worth its weight in gold. Ten, by comparison, is a klutz: it does halves and fifths and then gives up. Sixty is the number that always divides.
03 · The finger trickHow you might count to 60 on two hands
There is a lovely story for how they landed on 60 in the first place, and it starts with your own hands. Ignore the thumb on one hand and look at the other four fingers. Each has three little bones, three joints. Use your thumb as a pointer and you can tap out twelve joints on one hand alone. Now every time you reach twelve, raise a finger on the other hand to keep score. Five fingers, five lots of twelve, and twelve times five is exactly 60. One hand does the small counting, the other holds the tally, and you have counted to sixty without a single pebble or mark.
It is a beautiful idea, and finger-joint counting really is still used across parts of the Middle East and Asia today. But honesty matters more than a tidy story: this is a plausible reconstruction, not a proven fact. Nobody left us a Babylonian note saying “this is how we did it.” So treat it as the best guess for a mystery whose true answer is lost, not as gospel.
The 24-hour day is not a Babylonian invention at all. It was smuggled in from a completely different civilisation, and its hours were not even the same length twice.
04 · Enter EgyptWhy the day has 24 hours, not 60
Here is where two ancient worlds quietly merge on your clock face. The minutes and seconds are Babylonian, base 60. But the hours come from Egypt, and they run on 12. The Egyptians tracked the night by the stars, dividing the sky into groups called decans that rose one after another as the hours passed. Across a night, twelve of these star-groups did their turn, and so the night got carved into twelve parts. Pair that with twelve parts of daylight, and you have the 24-hour day, half of it written in the stars. Two civilisations, two number habits, one clock.
05 · The stretchy hourWhen a summer hour was longer than a winter one
Now for the part that genuinely bends the brain. For most of human history, an hour was not a fixed length. The Egyptians, and the Greeks and Romans after them, split the daylight into twelve hours no matter how much daylight there was. Which means in high summer, with the sun up for ages, each daytime hour was long. In deep winter, with a stingy little day, each one was short. These were called seasonal hours, and a summer daytime hour could be half as long again as a winter one. Your “hour” literally breathed with the seasons.
What killed the stretchy hour was a machine. When the mechanical clock spread through medieval Europe, it did the one thing the sundial never could: it ticked at a perfectly steady rate, indifferent to the season. A gear does not know it is July. So the fixed, equal hour we now take for granted is not some ancient truth. It is a fairly recent settlement, forced on us by the technology of the clock itself.
06 · The namingWhy it's called a 'minute' and a 'second'
The names are a giveaway, once you know what to listen for. When astronomers wanted to chop the hour into finer pieces, they used Babylonian base 60. Divide the hour by sixty and you get the “first small part,” in Latin the pars minuta prima. Say that quickly enough, for long enough, and it wears down to minute. Now divide that by sixty and you reach the “second small part,” the pars minuta secunda, which shortened all the way down to plain second. Your “second” is quite literally named after being the second thing you divided. The Greek astronomers Hipparchus and Ptolemy did the dividing; the snappy Latin names came later, in the medieval translations of Ptolemy’s great work, the Almagest.
07 · The long reachIt's not just clocks
Once you can see base 60, you find it everywhere. A circle has 360 degrees, which is simply six sixties. Each degree splits into 60 arcminutes, and each arcminute into 60 arcseconds, the exact same nesting as the clock, which is why the units even share the words “minute” and “second.” Every map coordinate, every line of latitude and longitude, is quietly counted in Babylonian. Attempts to overthrow it have flopped: Revolutionary France tried decimal time in the 1790s, with 10-hour days and 100-minute hours, and it collapsed within a couple of years because nobody could stand it. Base 60 is welded into civilisation too deeply to prise out.
08 · The payoffThe second broke free of the Earth
And here is the final twist, the one that closes the loop. For thousands of years, the whole point of a second was that it was a slice of a day, a piece of the Earth turning once on its axis. But it turns out the Earth is a sloppy timekeeper. Its spin speeds up and slows down by tiny, unpredictable amounts, so a second built on the day was never quite constant. So in 1967, we cut the cord. The second is now defined by an atom of caesium, as exactly 9,192,631,770 oscillations of the radiation it gives off. It no longer refers to the sky at all. So your clock is two things at once: minutes and seconds counted in a system four thousand years old, ticking to the beat of a single atom that does not care that the Earth exists. A dead empire set the pattern. A caesium atom now keeps the time.
Quick questions
Why does an hour have 60 minutes instead of 100?
Because the number came from the Babylonians, who counted in base 60, not base 10. Sixty divides evenly into halves, thirds, quarters, fifths and sixths, which made fractions of an hour easy long before anyone had a decimal point. When France tried to decimalise time in the 1790s, with 100-minute hours, people simply ignored it and it was dropped.
Why did the Babylonians use base 60?
They inherited it from the earlier Sumerians, and its great advantage is that 60 is the smallest number divisible by 1, 2, 3, 4, 5 and 6. In an age of fractions rather than decimals, that made it wonderfully flexible for splitting quantities, trading and astronomy. Exactly why the Sumerians first landed on 60 is not settled, but its divisibility is why it stuck.
Is it true they counted 60 on their fingers?
That is one popular hypothesis, and it is plausible but unproven. The idea: use the thumb of one hand to count the three joints on each of the other four fingers, which gives 12, then use the five fingers of the other hand to count up twelves, and 12 times 5 is 60. It is a neat reconstruction, and finger-joint counting really is still used in parts of the Middle East and Asia, but there is no direct evidence this is how base 60 actually began.
Why does a day have 24 hours?
That is a separate, Egyptian idea, not a Babylonian one. The Egyptians divided the night using decan stars, groups of stars that rose in sequence, and counted 12 of them across the night. They paired that with 12 hours of daylight, giving 24 in all. So the day's structure and the hour's subdivisions come from two different civilisations.
Were an hour's minutes always the same length?
No, and this surprises people. For most of history the 12 daytime hours were seasonal: daylight was split into 12 no matter how long the day was, so a summer daylight hour was genuinely longer than a winter one. Fixed, equal hours only became the norm with the spread of the mechanical clock in medieval Europe, which could not easily stretch and shrink its hours to match the season.
Where do the words 'minute' and 'second' come from?
From Latin. When astronomers subdivided the hour by 60, the first division was the pars minuta prima, the 'first small part', which became 'minute'. Divide again by 60 and you get the pars minuta secunda, the 'second small part', which became simply 'second'. The name literally records that it is the second-level subdivision.
Was it Ptolemy who invented minutes and seconds?
Not the words, but the method. The Greek astronomers Hipparchus and, later, Ptolemy used Babylonian base 60 to subdivide circles and angles into sixtieths and sixtieths-of-sixtieths. The Latin names 'pars minuta prima' and 'pars minuta secunda' actually appear later, in the medieval Latin translation of Ptolemy's Almagest. Ptolemy himself wrote in Greek and called them the 'first' and 'second' sixtieths.
Why are there 360 degrees in a circle, and does that relate to time?
Yes, it is the same base-60 habit. The Babylonians divided the circle into 360 degrees, and 360 is 6 times 60. Each degree splits into 60 arcminutes and each arcminute into 60 arcseconds, exactly mirroring minutes and seconds of time. Angles and clocks are cousins, both descended from Babylonian counting.
Why not switch to decimal time now?
It has been tried and it failed. Revolutionary France introduced decimal time in 1793, with 10 hours of 100 minutes each. It was logical but clashed with every clock, habit and schedule people already had, and it was abandoned within a couple of years. Base 60 is so deeply embedded in clocks, navigation and daily life that the switching cost has always outweighed the tidiness.
Why is the second now defined by an atom instead of the Earth?
Because the Earth is an unreliable clock. Its rotation speeds up and slows down slightly and unpredictably, so a second defined as a fraction of a day is not perfectly constant. Since 1967 the second has been defined instead by the caesium-133 atom, as exactly 9,192,631,770 oscillations of its radiation, which is astonishingly stable and can be measured anywhere.
What is a leap second?
It is a one-second adjustment occasionally added to clocks to keep atomic time roughly in step with the slightly wobbly rotation of the Earth. Because the two drift apart, timekeepers have inserted the odd extra second since 1972. It is a small patch over the gap between the perfect atomic second and the imperfect astronomical day.
Did the Babylonians actually measure minutes and seconds of time?
Not in daily life. They used base 60 mainly for astronomy and mathematics, dividing angles and celestial positions into sixtieths. Splitting the ordinary hour into 60 minutes and 3,600 seconds of time came much later, once clocks were accurate enough for such fine divisions to mean anything. The number system came first by thousands of years, the tiny time units came last.
Why 60 and not 12, if 12 is where the finger-joint idea starts?
The two work together. Twelve is already a very divisible number (into halves, thirds, quarters and sixths), and multiplying it by 5 gives 60, which adds fifths to the list and covers every whole number from 1 to 6. So 60 is best thought of as a super-divisible extension of 12, which is also why 12 shows up in the hours of the day and 60 in their subdivisions.
Is base 60 used anywhere else today?
Yes, and you use it constantly without noticing. Clocks (60 seconds, 60 minutes), the 360-degree circle, and the coordinates on a map, latitude and longitude in degrees, arcminutes and arcseconds, all run on base 60. It is one of the oldest human inventions still in everyday global use, older than the alphabet you are reading this in.
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