Ctesias, also known as Ctesias of Cnidus, was a Greek physician and historian from the town of Cnidus in Caria, then part of the Achaemenid Empire.

Knidos or Cnidus was a Greek city in ancient Caria and part of the Dorian Hexapolis, in south-western Asia Minor, modern-day Turkey. It was situated on the Datça peninsula, which forms the southern side of the Sinus Ceramicus, now known as Gulf of Gökova. By the 4th century BC, Knidos was located at the site of modern Tekir, opposite Triopion Island. But earlier, it was probably at the site of modern Datça.