Celsus, a celebrated Roman physician of the age of Augustus, and perhaps later; famed as the author of "De Medicina," a work often referred to, and valuable as one of the sources of our knowledge of the medicine of the ancients.

Celsus, a philosopher of the 2nd century, and notable as the first assailant on philosophic grounds of the Christian religion, particularly as regards the power it claims to deliver from the evil that is inherent in human nature, inseparable from it, and implanted in it not by God, but some inferior being remote from Him; the book in which he attacked Christianity is no longer extant, only quotations from it scattered over the pages of the defence of Origen in reply.