thumb|Ctesibius' water clock, as visualized by the 17th-century French architect [[Claude Perrault]]
Ctesibius or Ktesibios or Tesibius (; BCE) was a Greek inventor and mathematician in Alexandria, Ptolemaic Egypt. Very little is known of Ctesibius' life, but his inventions were well known in his lifetime. in early mentions and reference to his work, including by Vitruvius () in . He began his career as a barber, following his father.
Commemoration
- In 1976, the crater on the far side of the Moon was named Ctesibius by the International Astronomical Union.
- In 1897, the genus of a soft-bodied plant beetle, was named Ctesibius by Champion, and has one described species called the Ctesibius, C. eumolpoides.
Notes
thumb|417x417px|A reconstruction of the counterweight-adjustable mirror of Ctesibius in [[Museum of Ancient Greek Technology|Kotsanas Museum of Ancient Greek Technology, Athens, Greece.]]