I had a question that I can't find a straight answer to. I'm looking for information about the Catholic Church's claim to be the "original" form of Christianity. I've read that Catholics believe that St. Peter was given authority by Jesus to start the first church and become the first pope but I seriously doubt this is the case because of the numerous forms of Christianity that flourished within the first century after Jesus' alleged death. They didn't know which set of beliefs was the most accurate then so I doubt a few thousand years later these claims of authority are any more legit today.
With all of the gnostics and other branches of Christianity where does Catholicism fit, and when exactly was it created? I've read a range of dates, from St. Peter (according to the Catholics) to 312 when Emperor Constantine said he had a vision to unite all of Rome under one religion.