A clepsydra, also known as a water clock, is an ancient timekeeping device that measures time through the flow of water. It typically consists of a container that allows water to drip at a constant rate, with markings to indicate the passage of time. This method was used by various civilizations, including the Ancient Egyptians and Greeks, to track hours and minutes. The design of a clepsydra can vary, but it generally includes an upper reservoir that fills with water and a lower chamber where the water exits. As the water level decreases, the time elapsed can be read from the scale. Clepsydras were particularly useful in situations where traditional sundials were ineffective, such as during cloudy days or at night.