Emperor Theodosius I made Christianity the official state religion of Rome in the 380s, and outlawed worship in Pagan Temples in 391. He did this, because he felt himself Christianity was the right religion.
For those saying it was Constantine: While he himself converted to Christianity he did not adopt it for the Roman Empire. He only converted. It wasn't until Emperor Theodosius that the Roman Empire officially became Christian.
Circa 300 when Emperor Constantine - a murderer and vicious politician - declared himself "Pontifex Maximus" copying the custom the Jews had of naming one Holy Priest, he declared himself Maximus. Such arrogance. He ended up like he lived.
The Roman Emperor Constantine produced the bible and he was a pagan not god! He took the Jewish religion and basing it on the Mithras religion, organized it into Christianity and then into the Holly Roman Catholic Church!! Not in Israel or any of the countries of supposed origin but entirely ITALIAN!
Not one word of it is contemporary with the period and was not written until several hundred years after the period the story is set in!! How did the apostles write their books more than a hundred years after they would have been dead?
What a wonder full disinformation and deception campaign he waged against his Jewish enemies by turning them into his invented Christianity - so good in fact that Christians are still following the deception to this day!