Against Celsus is a classic work of Christian apologetics written by Origen of Alexandria in the 3rd century AD. The book is a response to Celsus's "True Word," a treatise that attacked Christianity on a number of grounds, including its irrationality, its lack of patriotism, and its acceptance of sinners. Origen's response is a comprehensive and detailed defense of Christianity, in which he argues for the rationality of Christian doctrine, the ethical superiority of Christian morality, and the universality of the Christian message. Against Celsus is an important source for the study of early Christianity and the development of Christian thought.