When did Christianity become a leading religion?

Answer 1

Christianity is said to have been founded in the first century CE. I grew slowly throughout the Roman Empire until, at the beginning of the 4th century, it probably consisted about ten percent of the population.

At this point, Emperor Constantine gave the proto-Catholic-Orthodox branch of Christianity state patronage. This patronage made Christianity socially and politically desirable for some, and the religion grew quite rapidly. In the decade of the 380s, Christianity was made the state religion, and in 391 CE pagan worship was banned.

So, Christianity became a leading religion in the fourth century CE.