Final answer:
Constantine played a pivotal role in Christianity's rise in the Roman Empire, issuing the Edict of Milan in 313 to legalize it, but Christianity became the official religion of Rome after his reign, under Emperor Theodosius I, by the end of the fourth century.
Step-by-step explanation:
Which Emperor Adopted Christianity in Rome?
The emperor who adopted Christianity as the state religion of Rome was not Emperor Constantine, but this happened by the end of the fourth century. Constantine played a pivotal role in Christianity's path to becoming the dominant religion of the Roman Empire, but the official state religion status was achieved after his reign. Constantine's notable actions regarding Christianity include the issuance of the Edict of Milan in 313, which guaranteed religious toleration and the legalization of Christianity, not making it the official religion.
Constantine believed in using Christianity as a means of unifying the empire and during his reign, he favored this religion leading to its expansion throughout the Empire. It wasn't until the year 380 AD, under the emperor Theodosius I, that Christianity became the official state religion of the Roman Empire.