Against Celsus (Greek: Κατὰ Κέλσου; Latin: Contra Celsum), preserved entirely in Greek, was Origen's last treatise, written about 248. It is an apologetic work defending orthodox Christianity against the attacks of the pagan philosopher Celsus, who was seen in the ancient world as early Christianity's foremost opponent. In 178, Celsus had written a polemic entitled On the True Word, in which he had made numerous arguments against Christianity. The church had responded by ignoring Celsus's attacks, but Origen's patron Ambrose brought the matter to his attention. Origen initially wanted to ignore Celsus and let his attacks fade, but one of Celsus's major claims, which held that no self-respecting philosopher of the Platonic tradition would ever be so stupid as to become a Christian, provoked him to write a rebuttal.
