Christianity is thought of as a religion of peace. But this episode reveals something different. The investigation begins with a mysterious symbol found engraved on an ancient skull. The film then discovers the same symbol on the walls of Roman army barracks and on pillars of underground churches. From Pompeii to the farthest reaches of the Empire, this episode reveals how Christianity secretly thrived within the very army that was supposed to suppress it.

Secrets of Christianity brings the techniques of investigative journalism to history, with Simcha Jacobovici connecting the dots of many academic and scientific disciplines to present a new take on the past. The series uncovers alternate truths that have either eluded us, or been kept from us – until now.