First, let me say that Carotta at times tries too much. This harms his thesis more than it helps it.
However, how unlikely it may sound at first, Carotta's case is very strong. He shows how through linguistic misinterprations of early versions of what we now know as the bible, which were written in several languages with comments in others, names, places and regular words were wrongly communicated to the followers of the then very young faith.
Some of the more poetic coincidences (and to Carotta's credit, he only mentions these as an afterthought) these include Jesus' birth exactly 100 years after Caesar's, Jesus' death exactly one easter-cycle after the introduction of the Julian calender (done by Caesar), Caesar's arrival in Egypt (tripping and falling on the beach, stretching out his arms and saying "I've got you, Africa") as a pope's visit prototype, Caesar's arrival in Rome, once, where he climbed the stairs of the Capitol on his knees after his chariot broke down right infront of it as a prototype for many pilgrimages. But as said, Carotta only mentions these examples as an afterthought.
Carotta extensively compares the life of Caesar with the supposed life of Jesus and easily shows through the many parallels and the many misspellings that the latter was created out of the former. Divus Iulius (Caesar worshipped as God) is the Christian God as well as Jesus. Octavianus (Augustus), Ceasar's adopted son, is also the son of God and therefore Jesus. Antonius, who fought with Octavianus for the legacy of Caesar, is Petrus and, on most occasions, Cleopatra is Maria Magdalena.
Carotta even goes a bit further, suggesting the possibility that Islam too is based on the Divus Iulius cult, not accepting Octavianus as the sun of god and even allows for the possibility that Buddhism is based on the distorted Divus Iulius cult the Bactrian Greeks brought with them to India.
The book's a tour de force and, at times, tiring to read. Carotta does manage to communicate his vision reasonably clearly. This, compared with the almost unbelievable thesis makes for a very intersting book.