How People Kept Time Before Clocks

Lacking sophisticated instruments, early humans kept time by observing the cosmos. “The oldest forms of timekeeping are all things that involved looking up at the sky,” says Chad Orzel, an associate professor of physics and astronomy at Union College in New York and author of A Brief History of Timekeeping: The Science of Marking Time, from Stonehenge to Atomic Clocks.

Some stars, such as Sirius, the brightest star in the night sky, took on particular importance in timekeeping. The ancient Egyptians associated the reappearance of Sirius each summer with the Nile River’s annual floods. The ancient Greeks, on the other hand, associated the return of Sirius—part of the dog constellation Canis Major—with the hottest and muggiest days of the year, giving rise to the expression “the dog days of summer.”

“There’s a lot of information in the patterns of the stars,” Orzel says. “That’s why astrology is a huge deal for thousands upon thousands of years.”

Even Stone Age peoples may have had timekeeping devices. A roughly 20,000-year-old animal bone, found in present-day Democratic Republic of the Congo, is etched with what appears to be three rows of tally marks. Some experts speculate that these markings represent a rudimentary lunar calendar, possibly used by women to track their menstrual cycles. Others believe the Ishango Bone, as it’s called, was a mathematical tool, akin to a very early calculator.

The Ishango Bone is not one of a kind. Even older tally sticks with a possible timekeeping function include the so-called Lebombo bone from present-day Eswatini in southern Africa, and the so-called Wolf Bone from present-day Czech Republic.

Each winter solstice at Newgrange, a prehistoric monument in present-day Ireland, the rising sun shoots a beam of light through a long passage and into a chamber that otherwise remains dark. “It’s an extremely slow kind of clock,” Orzel says. “It ticks one time a year.” He points out, however, that for a Neolithic agrarian society, knowing the shortest day of the year would have been “critically important information.”

Stonehenge, nearby Woodhenge, and other monuments throughout Britain and Ireland likewise align with the solstices or equinoxes. In fact, timekeeping monuments can be found throughout the world, including the Chankillo complex in Peru, the Wurdi Youang stone ring in Australia, Chichén Itzá in Mexico, Nabta Playa in Egypt and Angkor Wat in Cambodia.

“[Almost] every culture that we have any record of has done some sort of astronomical timekeeping in a way that leaves monumental architecture behind,” Orzel says.

Modern structures can serve much the same purpose. In New York City, crowds gather each year to observe “Manhattanhenge,” a term coined by astrophysicist Neil deGrasse Tyson for when the rising or setting sun aligns with Manhattan’s street grid.

While big monuments tracked the time of year, sundials tracked the time of day (and helped determine the time of year as well). “The technology needed to make a sundial is so rudimentary,” Orzel says. “Any big thing that casts a shadow can work as a sundial.”

Humans are presumed to have been telling time with shadows for many millennia, with ancient Egypt providing some of the best-known examples. Egyptian obelisks may have functioned as a type of shadow clock as early as 3500 B.C. The oldest surviving true sundials—replete with pointers and dials—date to around 1500 B.C., not long after the Egyptians came up with the concept of the 24-hour day.

Sundials were likewise used in ancient Rome, Greece, Carthage, China, the Middle East and elsewhere. Elaborate sundials still grace many public places worldwide, and garden sundials remain popular as well.

Sundials don’t work at night or when it’s cloudy, so that’s when water clocks—a timepiece in which water flows out of a container at a constant rate—proved most useful. An ancient Egyptian court official took credit for inventing them in the 16th century B.C., according to a tomb inscription from that time, and they spread from there to much of Europe and Asia.

Some water clocks, also known as clepsydras, were ornate works of art. They were also the “state-of-the-art timekeeper up to basically the start of the Renaissance,” Orzel says. He points out that they were more accurate than early mechanical clocks, which didn’t even have minute hands, and that Galileo Galilei used them as late as the 1600s to time objects in motion.

Chinese scientist Su Song developed a water-powered, proto-mechanical astronomical clock tower in the late 11th century, though it wasn't strictly a clepsydra.

Only after Dutch scientist Christiaan Huygens created the first pendulum clock in 1656 did water clocks become obsolete. The pendulum clock “really kickstarts precision timekeeping,” Orzel says. “It revolutionizes the field overnight.”

Because the viscosity of water changes depending on temperature, water clocks could not always be counted on to drip at the same rate. Water could also freeze if it got cold enough.

In the 10th century, Chinese engineer Zhang Sixun, who purportedly influenced Su Song’s work, got around this problem by using mercury in a clock instead of water. For much the same reason, mercury later came to be used in thermometers.

For seafaring peoples, timekeeping and navigation often went hand in hand. First invented over 2,000 years ago, the disc-shaped astrolabe, sometimes called the original smartphone, measured the height of celestial bodies above the horizon to determine latitude and time, among other functions. (Like all early navigation devices, astrolabes didn’t help much with longitude.)

“You get to the right latitude, and then you go east or west until you get where you want to go,” says P. Kenneth Seidelmann, a research professor in the University of Virginia’s astronomy department and co-author of Time: From Earth Rotation to Atomic Physics, describing how early sailors navigated.

Used throughout Europe and the Islamic world during the Middle Ages, the astrolabe was eventually replaced by the quadrant and sextant.

Incense has been used as a timekeeper in China since at least the sixth century, when poet Yu Jianwu wrote, “By burning incense [we] know the o’clock of the night, With graduated candle [we] confirm the tally of the watches.” In addition to incense sticks, marked off into equal intervals, the Chinese developed spiral incense coils and elaborately patterned seals for burning loose incense powder.

Also found in Japan and Korea, incense clocks operated in a variety of settings. An American diplomat recounted Chinese peasants being charged for water based on the amount collected while an incense stick burned. Incense timekeeping was likewise employed during emperor coronations, at geisha houses, on ships and as reminders for patients to take their medicine.

When different kinds of incense marked different periods of the day, a person could tell the time by smell alone. Incense could be an alarm clock as well. In one Chinese dragon boat design, incense burned through a silk thread at the allotted hour, dropping two bronze bells into a basin.

Into the 20th century, incense sticks timed the production of tea in Chinese factories and were carried by Chinese coal miners to measure how long to stay underground. “These incense sticks were very much premodern technologies, but they were used in very modern ways,” not unlike “a stopwatch in London at the same time,” says Andrew Liu, an associate professor of history at Villanova University, and author of Tea War: A History of Capitalism in China and India.

As Yu’s poem suggests, the Chinese also developed candle clocks, as did other civilizations. In ninth-century England, King Alfred the Great purportedly commissioned a six-candle clock to plan his day, with each candle designed to burn for about four hours. “It’s the same principle as incense,” Liu says. “Fire burns at a steady rate, so we can dependably use candles or incense to measure time.”

A knotted cord that burned like a wick or fuse was another fire-related timekeeping device. Chinese messengers were said to use them as alarm clocks, placing them between their toes and igniting them before falling asleep. When the lit cord touched their skin, they would awaken with a start.

A board game staple, the hourglass, in which sand or other fine particles drop from one chamber to another through a narrow opening, was “a remarkably late invention,” Orzel says. He explains that it’s not easy to seal sand in glass without it getting clumpy. “It’s a matter of being able to keep moisture out and not having it turn into a brick over a period of months,” Orzel says.

No documented evidence for the hourglass exists prior to 1338, when it was depicted on an Italian fresco. The first known weight-driven mechanical clock, by contrast, dates to 1283 in England. Yet because early mechanical clocks weren’t seaworthy, hourglasses remained a vital tool onboard ships for centuries.