Ctesibius was probably the first head of the Museum of Alexandria. Very little is known of his life but his inventions were well known. It is said (possibly by Diogenes Laertius) that his first career was as a barber. During his time as a barber, he invented a clever counterweight-adjustable mirror. His other inventions include the hydraulis, a water organ that is considered the precursor of the modern pipe organ, and an improved water clock called a clepsydra. The clepsydra kept more accurate time than any clock invented until the Dutch physicist Christiaan Huygens detailed the use of a pendulum to regulate a clock in the 17th century. He described the one of the first force pumps for producing a jet of water, or for lifting water from wells, and examples have been found at various Roman sites, such as at Silchester in Britain. The principle of the siphon has also been attributed to him.
According to Diogenes Laertius, Ctesibius was miserably poor. Laertius details this by recounting the following concerning the philosopher Arcesilaus:
Ctesibius's work is chronicled by Vitruvius, Athenaeus, and Philo of Byzantium who repeatedly mentions him, adding that the first mechanicians such as Ctesibius had the advantage of being under kings who loved fame and supported the arts. Proclus (the commentator on Euclid) and Hero of Alexandria (the last of the engineers of antiquity) also mention him.