The First Sexagesimal Clocks: Timekeeping Innovations of the Sumerians

When we glance at our watches or clocks today, we hardly think about the origins of the system that divides an hour into 60 minutes and a minute into 60 seconds. This familiar way of measuring time can be traced back thousands of years to the ancient civilization of the Sumerians. Situated in Mesopotamia, modern-day Iraq, the Sumerians developed one of the earliest known systems of writing, governance, and mathematics, including the sexagesimal (base-60) system. This system laid the groundwork for the first sexagesimal clocks, which profoundly influenced how we keep time today.

The Sumerians and the Birth of Civilization

The Sumerians are often credited with founding one of the world’s first civilizations around 4500 to 1900 BCE. They settled in the fertile region between the Tigris and Euphrates rivers, an area often referred to as the “cradle of civilization.” Here, they developed urban centers, complex societies, and various technological advancements.

Among their many achievements, the Sumerians are known for their contributions to writing, notably the cuneiform script, which is one of the earliest systems of writing. Their advancements in mathematics were equally groundbreaking, and the sexagesimal system is a prime example of their ingenuity.

The Sexagesimal System: Why Base 60?

The choice of base 60 may seem arbitrary to modern minds more accustomed to the decimal (base-10) system. However, the sexagesimal system has distinct advantages. Sixty is a highly composite number, meaning it has many divisors: 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, and 30. This makes it incredibly versatile for calculations and divisions, a feature that is especially useful in astronomy, geometry, and timekeeping.

The origins of the sexagesimal system are not entirely clear, but it is believed that the Sumerians inherited it from earlier cultures in the region. They refined and formalized the system, integrating it into various aspects of their daily life and scientific pursuits.

Timekeeping in Ancient Sumer

The Sumerians’ understanding of time was closely linked to their agricultural activities, religious practices, and astronomical observations. They needed a reliable way to measure time to organize their society, track the seasons, and conduct religious ceremonies. The development of the sexagesimal system facilitated more precise timekeeping.

The Sundial: Harnessing the Power of the Sun

One of the earliest timekeeping devices used by the Sumerians was the sundial. A sundial measures time based on the position of the sun’s shadow cast by a central gnomon (a vertical rod or stick). The Sumerians divided the day into 12 “double hours,” which were further divided into smaller units based on the sexagesimal system.

The design of the sundial allowed the Sumerians to estimate the passage of time during daylight hours. Although less effective on cloudy days or at night, the sundial was an essential tool for daily activities and ceremonies.

The Water Clock: Time Flowing Like Water

Another significant Sumerian invention was the water clock or clepsydra. This device measured time based on the regulated flow of water from or into a container. A typical water clock consisted of a stone vessel with a small hole at the bottom through which water dripped at a steady rate.


The Sumerians used water clocks to measure longer periods, such as night hours or intervals during the day when the sun was not visible. These clocks were especially useful for timing religious rituals and astronomical observations. The water clock’s reliance on the steady flow of water provided a more consistent measure of time than the sundial, albeit with its own limitations due to evaporation and changes in water flow.

The Legacy of Sumerian Timekeeping

The innovations in timekeeping by the Sumerians laid the groundwork for future advancements in horology (the study and measurement of time). Their use of the sexagesimal system influenced later civilizations, including the Babylonians, Greeks, and ultimately the entire world.

The Babylonians, who succeeded the Sumerians in Mesopotamia, continued to use and refine the sexagesimal system. They made significant contributions to astronomy and mathematics, many of which were based on the foundations laid by the Sumerians.

One of the most enduring legacies of Sumerian timekeeping is the division of an hour into 60 minutes and a minute into 60 seconds. This system was adopted and preserved through subsequent cultures and civilizations, eventually becoming the standard used worldwide today.

Sumerian Influence on Modern Timekeeping

The principles of Sumerian timekeeping can still be seen in our modern clocks and watches. The division of the day into 24 hours, each hour into 60 minutes, and each minute into 60 seconds is a direct legacy of the Sumerians’ sexagesimal system. This division facilitates the precise measurement of time, essential for everything from daily schedules to scientific research and global communications.

Furthermore, the Sumerians’ approach to mathematical calculations using the sexagesimal system has influenced various fields, including astronomy, navigation, and engineering. For example, the 360 degrees in a circle, a concept crucial for navigation and geometry, can be traced back to their innovations.

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