Ancient civilizations used water clocks to tell time by measuring the steady flow of liquid into or out of a container.

The oldest known water clock was found in the tomb of Pharaoh Amenhotep I in Egypt from around 1500 BCE. These devices allowed people to track time at night or on cloudy days when sundials did not work. Early versions were simple bowls with a hole in the bottom that let water leak out at a steady rate.In 325 BCE, Greek engineers added a float that rose as the water level changed. This float could turn gears to move a pointer on a dial, similar to the hands on a modern clock. Around 270 BCE, Ctesibius of Alexandria improved accuracy by creating a system that kept water pressure constant.In 1094 CE, a Chinese inventor named Su Song built a water-driven clock tower that was 40 feet tall. It used a chain-driven mechanism that worked like the parts found in later mechanical clocks. This tower could track the positions of stars and the time of day simultaneously.Water clocks were the most accurate way to tell time for over 2,000 years. Their accuracy was only limited by things like temperature changing the thickness of the water or dirt clogging the small holes. They were eventually replaced by pendulum clocks in 1656.