 Complete the following phrase:  Contra Celsum became the most influential of all early Christian apologetics works; before it was written, Christianity was seen by many as merely a folk religion for the illiterate and uneducated, but Origen raised it to a level of academic respectability. Eusebius admired Contra Celsum so much that in his Contra Hieroclem, he declared that Contra Celsum provided an adequate rebuttal to all criticisms the church would ever face. The compilers of the Philokalia in the fourth century AD relied extensively on Contra Celsum and almost one seventh of the entire text of the Philokalia is directly quoted from it. Basilios Bessarion 14031472, a Greek refugee who fled to Italy after the 