During excavations of a palace annex near the Weiyang Palace in Xi'an, archaeologists have unearthed the remains of a complex astronomical water-clock dating to the Western Han Dynasty. The device, which includes bronze siphons and a series of nested ceramic vessels, was used to track the passage of time with high accuracy to coordinate court rituals and celestial observations.
Unlike simpler clepsydras, this timepiece features a unique compensation tank to maintain steady water pressure, ensuring a constant flow rate. The discovery of inscribed wooden slips nearby details the training of "timekeepers" who were required to monitor the device 24 hours a day. This find provides the first physical evidence of the high level of horological technology achieved by Chinese engineers over two millennia ago.