Greek physician and historian of Persia and India whose works were popular and influential in antiquity. In 405 BC Ctesias traveled to the Persian court, where he remained as physician under the rulers Darius II (Darius II Ochus) and Artaxerxes II. He claimed to have treated Artaxerxes for wounds inflicted by his brother, Cyrus (Cyrus The Younger), at the Battle of Cunaxa (Cunaxa, Battle of) in 401 (an episode related by Xenophon in Anabasis, Book I).

Ctesias returned to Greece in 398 and began writing his Persica, a history of Assyria-Babylonia in 23 books. Books I–VI included a history of Assyria and the Medes, and the last 10 books were a more detailed account from the death of Xerxes (465) to 398. Although Ctesias claimed that his history was based on Persian archives and state records and therefore was far superior to Herodotus's history, what survives is full of romantic stories, exotic anecdotes, court gossip, and lists that are of dubious reliability. The work no longer exists, except in an abstract compiled by the patriarch Photius (Photius, Saint) of Constantinople (flourished c. AD 860). Ctesias also wrote a history of India (Indica) that was based on reports of Persian visitors and of Indian merchants and envoys to the Persian court. Although legendary and fabulous, it was the only systematic account of India until Alexander the Great's invasion of that country.