Celsus the Plantonist (c. 175-180 CE) was a pagan campaigner against Christianity towards the end of the second century. His works survive only as fragments incorporated into the writings of the early apologist Origen. [ce]
His writings are available in two translations: the dry Ante-Nicene Fathers works of Origen [or], and a more flowery (although less accurate [th]) version by R. J. Hoffmann [jm].
Celsus on Christianity
By the time of Celsus, the "miraculous" aspects of Christianity appear to have been firmly established. He poured scorn on the myths of Christianity, pointing out their obvious similarities with ancient pagan stories [jm]:
"Is your belief based on 'fact' that this Jesus told in advance that he would rise again after his death? That your story includes his predictions of triumphing over the grave? Well let it be so. Let's assume for the present that he foretold his resurrection. Are you ignorant of the multitudes who have invented similar tales to lead the simple minded hearers astray? It is said that Zamolix, Pythagoras' servant convinced the Scythians that he had risen from the dead, having hidden himself away in a cave for several years, and what about Pythagoras himself in Italy - or Phamsinitus in Egypt? Now then, who else: What about Orpheus among the Odrysians, Protesilaus in Thessaly, and above all Heracles and Theseus? But quite apart from all these risings from the dead, we must look carefully at the question of the resurrection of the body as a possibility given to mortals. Doubtless you will freely admit that these stories are legends, even as they appear to me; but you will go on to say that your resurrection story, this climax to your tragedy, is believable and noble."
"Are these distinctive happenings unique to the Christians - and if so, how are they unique? Or are ours to be accounted myths and theirs believed? What reasons do the Christians give for the distinctiveness of their beliefs? In truth there is nothing at all unusual about what the Christians believe, except that they believe it to the exclusion of more comprehensive truths about God."
The standard Apologetic response to Celsus is to point out that none of the pagan god-men listed by Celsus were crucified, or that second century paganism in fact borrowed much of its teachings from Christianity [tk]. Celsus would no doubt have been amused - since these arguments depend on the assumption that Christianity is "correct" and that every other belief system is a mythology!
The fact is that studies in comparative mythology have shown overwhelming parallels between Christianity and paganism in the second century CE, with both "religions" probably borrowing from common sources [rt].
Conclusion
There is a great deal of evidence that the concept of "Jesus Christ" as a historical figure does not seem to have been taken up by Christianity until around the time of Celsus [hg]. The fragments of his writings which survive throw a remarkable light on the development of early Christianity, and the obvious parallels it had with older pagan mythologies.
The Jesus Mysteries (excerpts) by Timothy Freke and Peter Gandy. (Celsus quotations are from R.J. Hoffmann, Celsus On The True Doctrine, Oxford University Press, 1987) [jm]
"In his comments, Celsus attempts impartiality: He is no admirer of Judaism ['runaway Egyptian slaves who have never done anything worth mentioning'] but acknowledges the antiquity of Jewish teaching and juxtaposes it with the newness of Christian doctrine. He thinks Christian teachers are no better than the begging priests of Cybele and the shysters of popular religions. Importantly, Celsus does not dwell on the impurity of Christian ritual (though he alludes to it), but emphasizes that Christians are sorcerers like their founder, that they lack patriotism, and that every Christian church is an illegal association which exists not because their God arranges it (thus Tertullian), but because the emperor does not choose to stamp them out entirely." - Porphyry's Against the Christians: The Literary Remains, R. Joseph Hoffman
Further Reading
Quoting Celsus, extracts from Celsus On the True Doctrine, translated by R. Joseph Hoffman, Oxford University Press, 1987.