How did the first clockmaker know the right time? The answer lies in the Sun, water and stars

Today, checking the time is almost instinctive. A glance at a phone, smartwatch or wall clock can tell us the hour, minute and even second. But for most of human history, there was no clock to consult. So when the first mechanical clocks appeared, how did their makers know what time they were supposed to show?

The answer goes back far beyond gears and springs. The first clockmakers did not invent timekeeping—they inherited a system humans had already built by watching the sky.

Long before mechanical clocks, people measured time through recurring natural events. The movement of the Sun across the sky, the phases of the Moon and the changing position of stars provided the earliest reference points. Archaeological evidence suggests that humans were tracking lunar cycles thousands of years ago.

Sun was humanity's first clock

The simplest daytime timekeeper was the shadow cast by the Sun. Sundials used a fixed object, or gnomon, whose changing shadow indicated the passage of the day.

Ancient Egyptians developed sundials thousands of years ago and divided daylight into hours. Over time, sundials became increasingly sophisticated, with different designs accounting for seasonal changes in the Sun's position.

But the system had an obvious weakness: the Sun disappears at night, and clouds can make a sundial useless. That led to another ingenious solution — water.

Water clocks kept ticking after sunset

Water clocks, or clepsydras, measured time through the controlled movement of water. A container could slowly drain or fill, with markings indicating the passage of predetermined intervals.

One of the oldest known examples comes from ancient Egypt, while Greek and Roman engineers later developed increasingly elaborate versions. Some water clocks incorporated floats, moving indicators, bells and astronomical displays.

The system was not perfect. Water does not flow at exactly the same rate throughout the draining process, making precision difficult. Temperature and other physical conditions could also affect performance.

Other civilizations experimented with sandglasses, candle clocks and oil lamps, essentially turning predictable physical processes into timers.

So what did the first mechanical clock copy?

It did not simply copy the position of a sundial's shadow.

Instead, clockmakers had to translate an established astronomical understanding of the day into a machine. By the medieval period, people already had accepted divisions of the day and established ways of determining them. Mechanical clocks provided a new way of reproducing those divisions without depending directly on sunlight or flowing water.

The first large mechanical clocks appeared in Europe during the first half of the 14th century. They were weight-driven and used mechanisms such as the verge-and-foliot escapement to regulate their movement.

Historical evidence also points to earlier sophisticated clock technology outside Europe. Chinese engineers, for example, developed elaborate water-powered astronomical clock mechanisms centuries earlier, including the celebrated clock tower associated with Su Song in 1088.

First mechanical clocks were hardly precise

The idea of a mechanical clock can sound synonymous with accuracy. Early clocks were anything but.

Early European mechanical clocks could be accurate to only around 15 minutes per day — roughly comparable to a good sundial. They initially did not even need minute hands.

Spring-driven mechanisms made clocks smaller and portable, while Christiaan Huygens' pendulum clock in the 17th century dramatically improved precision.

That evolution changed more than clocks. More reliable timekeeping helped societies coordinate religious observances, trade, work and eventually transportation and navigation.