Ctesibius or Ktesibios or Tesibius (; fl. 285–222 BC) was a Greek inventor and mathematician in Alexandria, Ptolemaic Egypt. He wrote the first treatises on the science of compressed air and its uses in pumps (and even a cannon). This, in combination with his work on the elasticity of air On pneumatics, earned him the title of "father of pneumatics." None of his written work has survived, including his Memorabilia, a compilation of his research that was cited by Athenaeus.
Ctesibius is a small lunar impact crater that is located near the equator, on the far side of the Moon. It lies between the larger crater Abul Wáfa to the west and the slightly smaller Heron to the east.
The outer wall of Ctesibius is wide and sharp-edged, with little erosion. A low ridge is attached to the southern rim, and curves to the south-southeast. At the center of the relatively flat interior is a low ridge. Faint traces of ray material lies across the western floor and rim from Necho to the southeast.