The first six books covered the history of Assyria and Babylon to the foundation of the Persian empire; the remaining seventeen went down to the year 398 BC. Of the two histories, we possess abridgments by Photius, and fragments are preserved in Athenaeus, Plutarch, Nicholas of Damascus and especially Diodorus Siculus, whose second book is mainly from Ctesias. As to the worth of the Persica there has been much controversy, both in ancient and modern times. Although many ancient authorities valued it highly, and used it to discredit Herodotus, a modern author writes that "(Ctesias's) unreliability makes Herodotus seem a model of accuracy." Ctesias's account of the Assyrian kings does not reconcile with the cuneiform evidence.
Ctesias was a Greek physician and historian from Cnidus in Caria. Ctesias, who lived in the 5th century BC, was physician to Artaxerxes Mnemon, whom he accompanied in 401 BC on his expedition against his brother Cyrus the Younger. Ctesias was the author of treatises on rivers, and on the Persian revenues, of an account of India entitled Indica (which is of value as recording the beliefs of the Persians about India), and of a history of Assyria and Persia in 23 books, called Persica, written in opposition to Herodotus in the Ionic dialect, and professedly founded on the Persian royal archives.