Water clock in the context of "Horology"

The history of timekeeping devices dates back to when ancient civilizations first observed astronomical bodies as they moved across the sky. Devices and methods for keeping time have gradually improved through a series of new inventions, starting with measuring time by continuous processes, such as the flow of liquid in water clocks, to mechanical clocks, and eventually repetitive, oscillatory processes, such as the swing of pendulums. Oscillating timekeepers are used in modern timepieces. Sundials and water clocks were first used in ancient Egypt c. 1200 BC and later by the Babylonians, the Greeks and the Chinese. Incense clocks were being used in China by the 6th century. In the medieval period, Islamic water clocks were unrivalled in their sophistication until the mid-14th century. The hourglass, invented in Europe, was one of the few reliable methods of measuring time at sea.

In medieval Europe, purely mechanical clocks were developed after the invention of the bell-striking alarm, used to signal the correct time to ring monastic bells. The weight-driven mechanical clock controlled by the action of a verge and foliot was a synthesis of earlier ideas from European and Islamic science. Mechanical clocks were a major breakthrough, one notably designed and built by Henry de Vick in c. 1360, which established basic clock design for the next 300 years. Minor developments were added, such as the invention of the mainspring in the early 15th century, which allowed small clocks to be built for the first time.

A clock or chronometer is a device that measures and displays time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month, and the year. Devices operating on several physical processes have been used over the millennia.

Some predecessors to the modern clock may be considered "clocks" that are based on movement in nature: A sundial shows the time by displaying the position of a shadow on a flat surface. There is a range of duration timers, a well-known example being the hourglass. Water clocks, along with sundials, are possibly the oldest time-measuring instruments. A major advance occurred with the invention of the verge escapement, which made possible the first mechanical clocks around 1300 in Europe, which kept time with oscillating timekeepers like balance wheels.

The incense clock (simplified Chinese: 香钟; traditional Chinese: 香鐘; pinyin: xiāngzhōng; Wade–Giles: hsiang-chung; lit. 'fragrance clock') is a timekeeping device that originated from China during the Song dynasty (960–1279) and spread to neighboring East Asian countries such as Japan and Korea. The clocks' bodies are effectively specialized censers that hold incense sticks or powdered incense that have been manufactured and calibrated to a known rate of combustion, used to measure minutes, hours, or days. The clock may also contain bells and gongs which act as strikers. Although the water clock and astronomical clock were known in China (example: Su Song), incense clocks were commonly used at homes and temples in dynastic times.

The Song dynasty (Chinese: 宋朝; 960–1279 CE) witnessed many substantial scientific and technological advances in Chinese history. Some of these advances and innovations were the products of talented statesmen and scholar-officials drafted by the government through imperial examinations. Shen Kuo (1031–1095), author of the Dream Pool Essays, is a prime example, an inventor and pioneering figure who introduced many new advances in Chinese astronomy and mathematics, establishing the concept of true north in the first known experiments with the magnetic compass. However, commoner craftsmen such as Bi Sheng (972–1051), the inventor of movable type printing (in a form predating the printing press of Johannes Gutenberg), were also heavily involved in technical innovations.

The ingenuity of advanced mechanical engineering had a long tradition in China. The Song engineer Su Song, who constructed a hydraulically-powered astronomical clocktower, admitted that he and his contemporaries were building upon the achievements of the ancients such as Zhang Heng (78–139), an astronomer, inventor, and early master of mechanical gears whose armillary sphere was automatically rotated by a waterwheel and clepsydra timer. The application of movable type printing advanced the already widespread use of woodblock printing to educate and amuse Confucian students and the masses. The application of new weapons employing the use of gunpowder enabled the Song to ward off its militant enemies—the Liao, Western Xia, and Jin with weapons such as cannons—until its collapse to the Mongol forces of Kublai Khan in the late 13th century.

The Tower of the Winds, known as the Ωρολόγιο του Κυρρήστου in Greek, and by other names, is an octagonal Pentelic marble tower in the Roman Agora in Athens, named after the eight large reliefs of wind gods (in the form of young winged men and old men) around its top. Its date is uncertain, but was completed by about 50 BC, at the latest, as it was mentioned by Varro in his De re Rustica of about 37 BC. It is "one of the very small number of buildings from classical antiquity that still stands virtually intact", as it has been continuously occupied for a series of different functions.

Formerly topped by a wind vane, it is the only surviving horologium or clock tower from classical antiquity. It also housed a large water clock and incorporated sundials placed prominently on its exterior faces; "citizens were thus able by using this building to orient themselves in space and time. Architecture, sculpture and the new science were perfectly integrated".