The History of Time
It’s time! Yes, today is about time. It’s about how humans began measuring it, how we came to live our lives by it, and why it’s structured the way it is in our current time. Welcome to Math! Science! History! I’m Gabrielle Birchak, and I have a background in math, science, and journalism. And today we’re going to take the time to learn about time!
What time is it? Simple question, right? You probably glanced at your phone or your kitchen microwave. But what if I told you that the way we tell time, the ticking seconds, the 60-minute hours, the 24-hour day, the 7‑day week, isn’t natural at all. In fact, it’s a patchwork of ancient customs, astronomy, politics, and religion.
THE FIRST TIMEKEEPERS
Long before clocks or calendars, humans observed the natural world. They followed the sun, the moon, and the seasons. These celestial cycles shaped their days, rituals, and migrations. However, once agriculture emerged around 12,000 years ago, precision was no longer a luxury; it was a matter of survival.
The story of timekeeping doesn’t begin with grand temples or bronze mechanisms; it begins in the Fertile Crescent, where people first settled permanently nearly 12,000 years ago, around 10,000 BCE. In what is now called Mesopotamia, a region later divided among Sumeria, Akkad, Babylonia, and Assyria. Here, small farming communities began to emerge along the Tigris and Euphrates Rivers. This was the Neolithic Revolution, during which humans transitioned from hunting and gathering to cultivating crops, domesticating animals, and constructing permanent homes. To plant, harvest, and store food successfully, these early settlers would have needed some construct of time. They likely observed the seasonal patterns of the sun and stars, marking cycles to guide their survival long before the advent of written history.
Over thousands of years, these practical observations became sophisticated systems. By the Uruk period (c. 4000–3100 BCE), Mesopotamian astronomer-priests had divided the sky into twelve equal zones, mapping the sun’s annual journey through what we now know as the constellations of the zodiac. They also developed the sexagesimal system, or base-60 mathematics, which is still with us today in our 60-minute and 60-second units. These divisions enabled them to measure not just seasons, but increasingly smaller increments of time, blending astronomy, mathematics, and record-keeping into a structured worldview.
Meanwhile, to the southwest, the civilization of ancient Egypt was taking shape. Although Egypt’s unification under a single ruler didn’t occur until around 3100 BCE, its methods of timekeeping were equally ingenious.
They developed a 365-day calendar, dividing it into twelve months of thirty days, plus five “epagomenal” days dedicated to the gods.[1] Using the heliacal rising of Sirius to predict the flooding of the Nile, they divided the day with shadow clocks and sundials. They used star risings at night, similar in spirit to Mesopotamian decans, to mark the passage of hours. Where Mesopotamia’s genius gave us the mathematical skeleton of time, Egypt tied it to the sun’s rhythm and the heartbeat of the Nile. Together, they laid the earliest foundations of the system we still live by today.
The Egyptians were among the first to formalize timekeeping. Their observations of the star Sirius rising just before dawn helped them predict the flooding of the Nile, a vital agricultural event.[2]
Hours? For that, we owe a debt to the Babylonians.
BASE-60 AND THE BABYLONIANS
The Greeks and Romans later inherited this model. By the time Hipparchus introduced equinoctial hours —12 equal parts for day and night, regardless of the season — the groundwork for our modern hour was laid.
Why are there 60 seconds in a minute, 60 minutes in an hour, and 360 degrees in a circle? These numbers seem arbitrary, but they’re not. They’re part of an ancient system called sexagesimal, or base-60.
The sexagesimal system originated in Mesopotamia and was developed by the Babylonians. The Babylonians lived over 4,000 years ago in Mesopotamia, modern-day Iraq. They inherited a powerful legacy from the Sumerians, and among their many achievements, which included writing, astronomy, and architecture, was a sophisticated number system based on the number 60.[3]
Now you might be wondering: why 60? Why not something simpler, like 10 or 100?
Well, 60 is a super composite number, meaning it has more divisors than any smaller number. Sixty can be evenly divided by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30. That makes it ideal for splitting things into parts, especially when you’re trying to divide hours, angles, or even property in a way that’s fair and flexible.
Imagine trying to divide an hour into two, three, four, or even five equal parts. Sixty can handle that without messy remainders.
But the sexagesimal system wasn’t just about time. The Babylonians used it in astronomy, mathematics, and commerce. On their clay tablets, they recorded massive calculations, star charts, and even algebraic equations, all in the base-60 system.[4]
One of their most famous tablets, Plimpton 322, is over 3,000 years old and contains what we would now recognize as Pythagorean triples, suggesting they understood principles of right-angle triangles long before Pythagoras did.[5]
And it was all written using a mix of base-60 for fractions and base-10 for counting whole numbers. Picture a hybrid system: they used a positional number system, meaning the place of a digit affected its value, just like we do with tens, hundreds, and thousands. However, theirs was far more advanced than what the Greeks and Romans had.
The Babylonians developed a place value system more than 1,500 years before we adopted it with Arabic numerals. They even used a placeholder symbol that acted a bit like our modern zero. However, it wasn’t exactly zero as we know it yet.[6]
Now, here’s where things get really interesting. Babylonian astronomers used base-60 math to divide the circle into 360 degrees, likely because the circle was associated with the year, and there are roughly 360 days in a year, if you round out the solar cycle. That division of the circle into 360 degrees stuck. And we still use it today in geometry, cartography, and navigation.
Likewise, the Babylonian method of dividing time into 12 double-hours (for a total of 24 hours), with each hour split into 60 minutes and each minute into 60 seconds, laid the groundwork for what became the standard in Greek, Islamic, and later European astronomical traditions.[7]
Even though we now operate in a decimal-based society, our currency, our calculators, and our computers have never really shaken off our Babylonian roots. Every time you glance at your watch, spin a compass, or measure an angle, you’re whispering a thank you to the mathematicians of ancient Mesopotamia.
So, yes, base-60 might seem odd today, especially if you’re used to the clean simplicity of decimal notation. However, when it comes to dividing, measuring, and mapping the world, it turns out that 60 is a kind of mathematical miracle. The Babylonians didn’t just give us a clock. They gave us a worldview, shaped by stars, logic, and timeless ingenuity.
THE ROMAN CALENDAR CHAOS
The early Roman calendar had only ten months, beginning in March. That’s why “September” means seven but is our ninth month today. Their system didn’t match the solar year and required constant tinkering.
In 46 BCE, Julius Caesar enlisted Egyptian astronomers to rectify the issue. The new calendar was primarily used for positive propaganda about Julius Caesar and to aid his military in seasonal attacks. It served as a military guide. Still, the results helped to adjust the calendar in a more accurate form. The result? The Julian calendar: 365 days with a leap year every four years. It brought much-needed stability.
Still, even the Julian calendar ran about 11 minutes longer than the solar year. After centuries, that added up.
As a quick side note, the Gregorian calendar was introduced in 1582 CE by Pope Gregory XIII as a reform of the Julian calendar. Its purpose was to correct the drift between the calendar year and the solar year caused by the Julian system’s slightly inaccurate calculation of the year’s length. The reform included adjusting the leap year rule, which states that if a year is divisible by 4, it is a leap year. But there is an exception to this. If it’s also divisible by 100, it is not a leap year. And there’s an exception to that exception; if it’s divisible by 400, it is a leap year after all. For the year 2000, if it’s divisible by 400, it’s a leap year. For the year 1900, which is divisible by 100 but not by 400, it is not a leap year. The year 2024, since it’s divisible by 4 but not 100 it’s a leap year.
This reform also realigned the calendar with the equinox by skipping 10 days in October 1582. But this really only applied to countries that adopted it immediately. And adoption wasn’t instant. Catholic countries, such as Italy, Spain, and Portugal, switched in 1582, but Protestant countries took decades or even centuries to adopt.
THE CLOCKS BEGIN TO TICK
Now let’s talk about clocks.
Before clocks, time was measured by the sky. People relied on natural rhythms: the sun rising and setting, the lengthening or shortening of days with the seasons, and the moon cycling through its phases. For thousands of years, these celestial patterns were enough. But as societies grew, rituals and responsibilities demanded something more precise, something measurable.
The earliest timekeepers weren’t mechanical at all. Think sundials, simple yet brilliant tools that use a shadow cast by a stick, or gnomon, to tell the hour based on the sun’s position in the sky.[8] The ancient Egyptians used sundials as early as 1500 BCE, dividing daylight into twelve equal parts. However, these only worked on sunny days and not at night.
So they built alternatives.
WATER, CANDLES, AND STARS: THE PRE-MECHANICAL AGE
Enter the water clock, or clepsydra, one of humanity’s oldest time-measuring instruments. The earliest versions date back to ancient Babylon, Egypt, and China.[9] These clocks worked by letting water drip from one vessel to another at a consistent rate. As the water level rose or fell, it could be calibrated to measure time intervals. Water clocks enabled time to be tracked after sunset, a significant leap.
In medieval China, Su Song’s astronomical clock tower, built in 1090 CE, combined water-powered mechanisms with gears and wheels, early evidence of what would become clockwork machinery.[10]
In Europe, monks turned to candle clocks and incense clocks, which burned at predictable rates. These weren’t precise by modern standards, but they were good enough for scheduling prayers. And that’s key: early timekeeping wasn’t for the general public. It was for religious purposes, especially in Christian monasteries, where monks were required to observe the Divine Office, a daily schedule of prayers that took place at set hours throughout the day and night. As a result, monasteries became the first official keepers of time.
THE BIRTH OF THE MECHANICAL CLOCK
Now comes a game-changer: the mechanical escapement.
Around the late thirteenth to early fourteenth century, European inventors began creating devices that used weights, gears, and escapements to regulate movement.[11] The escapement is what gave these machines their tick-tock rhythm. It allowed energy to escape in controlled bursts, pushing gears forward at a regular rate, essentially “dripping” mechanical time instead of water.
One of the earliest fully mechanical clocks was installed in Salisbury Cathedral, England, around 1386. It had no dial or hands, just a bell that rang at regular intervals.5 As a result, the first public clocks didn’t show time, they sounded it.
This made time a communal experience. Imagine a town square where everyone listens for the bell to signal the start of a prayer, a meal, or the end of the workday. Time became a shared rhythm, no longer hidden in the stars or inside monasteries.
THE RISE OF THE CLOCK FACE
But soon, we wanted more than bells. We wanted to see the time.
In the fourteenth and fifteenth centuries, clockmakers began adding faces to their machines, often with only one hand, the hour hand. That was enough for daily life, which didn’t demand minute-level precision. The minute hand came later, around the sixteenth century, as mechanisms became more refined.[12]
One of the most famous examples is the Prague Astronomical Clock, installed in 1410. Not only did it tell the hour, but it also showed the position of the sun and moon, the zodiac signs, and even included animated figures. Time wasn’t just visible, it was theatrical.7
As cities were filled with public clocks, time became centralized and standardized. It shaped work, trade, governance, and daily structure. No longer was time something internal or intuitive; it was externalized, measured, and managed.
THE PERSONALIZATION OF TIME
By the seventeenth century, advances in metallurgy and precision engineering had led to the development of spring-powered watches, which replaced weights and pendulums. The invention of the mainspring made clocks portable and personal.
The next major leap came with Christiaan Huygens and the pendulum clock, patented in 1656. It was accurate to within fifteen seconds per day, a stunning improvement at the time.[13] Then came marine chronometers, essential for navigation at sea, thanks to John Harrison in the eighteenth century. They allowed sailors to calculate longitude with precision, revolutionizing global exploration.
And just like that, time went from public towers to pocket watches, a symbol of sophistication and punctuality.
By the twentieth century, wristwatches became widespread, particularly during World War I, when soldiers needed easy access to the time without fumbling for a pocket watch. The personal clock was now standard. Everyone had their own little ticking universe.
TIME BECOMES DIGITAL
And then came the digital revolution.
In 1927, the first quartz clock was developed. Quartz oscillates at a consistent frequency when electrified, allowing for astonishing accuracy. These clocks didn’t rely on gears or pendulums; instead, they used electricity and crystal vibrations.
By the 1970s, quartz wristwatches were mass-produced and affordable. The once-elite instrument of kings and clergy has become everyday technology.
Today, we live by digital time, from our phones and computers to our microwaves and thermostats. We synchronize with atomic clocks, which count the vibrations of cesium atoms to define the second with unimaginable precision. What’s most fascinating about atomic clocks is that they are so accurate that they only lose about one second every 100 million years.[14]
WHEN TIME BECAME VISIBLE, AND INVISIBLE AGAIN
Ironically, though, as time has become more precise, it’s also become more invisible.
We don’t watch clocks anymore; we get notifications. Our devices update automatically. Coordinated Universal Time, or UTC, governs everything from GPS satellites to stock markets to your smartwatch’s alarm. The ticking is silent now. But the numbers are but a glow. However, the bells have been replaced by a downloaded ringtone song; specifically, the best-selling ringtone is T‑Pain’s “I’m N Luv (wit a stripper).” Okee dokee then! I’m not gonna judge.
But behind that glowing screen lies the work of millennia. Every tick of your digital watch is the echo of water flowing in clay jars, of monks striking bells, of astronomers charting the stars.
Time became visible when we learned to mechanize it, to share it, to own it. And in doing so, we transformed how we work, think, and live. Today, we live in a different time and world. Time is no longer a local affair because now we have time zones. And although it would make sense that we have 24-hour time zones because there are 24 hours in a day, we actually have more time zones. If you are interested in learning more about our time zones, stay tuned for this Friday’s Flashcards episode!
THE TICK OF THE ATOM
Fast forward to the twentieth century: Einstein’s theory of relativity showed that time isn’t absolute; it changes depending on speed and gravity.[15] Still, for everyday use, we needed consistency. In 1967, scientists defined the second using the cesium-133 atom. Atomic clocks now measure one second as 9,192,631,770 oscillations of a cesium atom. These clocks run everything from GPS to financial markets.
What this means is that when you check your phone, you’re looking at atomic time.
WHY THIS TIME STRUCTURE?
Why do we still live by 60-minute hours, 24-hour days, and 7‑day weeks? In truth, it’s less about logic and more about legacy. Once systems become embedded across cultures and continents, they become nearly impossible to unravel. Even when revolutions occurred opposing this system, such as when the French attempted to decimalize time with 10-hour days and 100-minute hours, they failed to uproot what tradition cements. We still wrestle with daylight saving time and leap seconds. Still, despite its quirks and contradictions, the structure we’ve inherited continues to shape our lives with remarkable endurance.
Because time, as we know it, isn’t something we discovered; it’s something we created. From sundials casting shadows in the sand to atomic vibrations measured in billionths of a second, humanity has spent millennia sculpting meaning from the silent flow of existence. In shaping time, we shaped ourselves, our rituals, our civilizations, our sense of order. So the next time you glance at the clock, remember: you’re not just reading numbers. You’re touching thousands of years of human curiosity, ingenuity, and tradition. You are in sync with history, living in the same great continuum as the countless lives that came before you. And in that moment, the choice is yours: to let time pass or to seize it. That being said, carpe diem, my friends!
[1] Geller, Mark, and Mark Ronan. 2014. “Friberg’s Remarkable Collection of Babylonian Mathematical Texts.” Wiener Zeitschrift for Die Kunde Des Morgenlandes 104: 233–40.
[2] Robson, Eleanor. 2008. Mathematics in Ancient Iraq: A Social History. Princeton University Press. https://doi.org/10.2307/j.ctv10qqzk0.
[3] Geller, Mark, and Mark Ronan. 2014. “Friberg’s Remarkable Collection of Babylonian Mathematical Texts.” Wiener Zeitschrift for Die Kunde Des Morgenlandes 104: 233–40.
[4] Robson, Eleanor. 2008. Mathematics in Ancient Iraq: A Social History. Princeton University Press. https://doi.org/10.2307/j.ctv10qqzk0.
[5] Neugebauer, Otto. The Exact Sciences in Antiquity. Dover Publications, 1969.
[6] Ifrah, Georges. The Universal History of Numbers: From Prehistory to the Invention of the Computer. Wiley, 2000
[7] Toomer, G.J. “Hipparchus.” In Dictionary of Scientific Biography, edited by Charles C. Gillispie. Scribner’s, 1970.
[8] Whitrow, G. J. 1989. Time in History : Views of Time from Prehistory to the Present Day. With Internet Archive. Oxford ; New York : Oxford University Press. http://archive.org/details/timeinhistoryvie0000whit.
[9] Aveni, Anthony F. 2002. Empires of Time : Calendars, Clocks, and Cultures. With University Press of Colorado. Boulder, Colo. : University Press of Colorado. http://archive.org/details/emporesoftimecal00anth.
[10] Needham, Joseph. Science and Civilization in China, Vol. 4: Physics and Physical Technology. Cambridge University Press, 1965.
[11] Dohrn-van Rossum, Gerhard. History of the Hour: Clocks and Modern Temporal Orders. University of Chicago Press, 1996.
[12] Landes, David S. Revolution in Time: Clocks and the Making of the Modern World. Harvard University Press, 1983.
[13] Huygens, Christiaan. Horologium Oscillatorium. Paris, 1673.
[14] National Institute of Standards and Technology (NIST). “How Accurate Are Atomic Clocks?” 2024.
[15] Einstein, Albert. Relativity: The Special and the General Theory. 1916.