State religion

=== Roman religion and Christianity ===
{{Main|Roman imperial cult|Christianity as the Roman state religion}}
In Rome, the office of ''[[Pontifex Maximus]]'' came to be reserved for the Emperor, who was occasionally [[Apotheosis|declared a god]] posthumously, or sometimes during his reign. Failure to worship the Emperor as a god was at times punishable by death, as the Roman government sought to link emperor worship with loyalty to the Empire. Many Christians and Jews were subject to persecution, torture and death in the Roman Empire because it was against their beliefs to worship the Emperor.{{Citation needed|date=March 2023}}

In 311, Emperor [[Galerius]], on his deathbed, declared a religious indulgence to Christians throughout the Roman Empire, focusing on the ending of anti-Christian persecution. [[Constantine I]] and [[Licinius]], the two ''[[Augustus (title)|Augusti]]'', by the [[Edict of Milan]] of 313, enacted a law allowing religious freedom to everyone within the Roman Empire. Furthermore, the Edict of Milan cited that Christians may openly practice their religion unmolested and unrestricted, and provided that properties taken from Christians be returned to them unconditionally. Although the Edict of Milan allowed religious freedom throughout the Empire, it did not abolish nor disestablish the Roman state cult (Roman polytheistic paganism). The Edict of Milan was written in such a way as to implore the blessings of the deity.{{Citation needed|date=March 2023}}

Constantine called up the [[First Council of Nicaea]] in 325, although he was not a baptized Christian until years later. Despite enjoying considerable popular support, Christianity was still not the official state religion in Rome, although it was in some neighboring states such as [[Kingdom of Armenia (antiquity)|Armenia]], [[Kingdom of Iberia (antiquity)|Iberia]], and [[Kingdom of Aksum|Aksum]].{{Citation needed|date=March 2023}}

[[Religion in ancient Rome|Roman religion]] ([[Neoplatonic]] [[Religion in ancient Greece|Hellenism]]) was restored for a time by the Emperor [[Julian (emperor)|Julian]] from 361 to 363. Julian does not appear to have reinstated the persecutions of the earlier [[Roman emperors]].{{Citation needed|date=March 2023}}

[[Catholic]] Christianity, as opposed to Arianism and other ideologies deemed [[heresy|heretical]], was declared to be the [[State church of the Roman Empire|state religion of the Roman Empire]] on 27 February 380<ref>{{cite web |title=The Theodosian Code |url=http://www.ancienttexts.org/library/latinlibrary/theod.html |work=The Latin Library at Ad Fontes Academy|publisher=Ad Fontes Academy |access-date=2006-11-23}}</ref> by the decree ''[[Edict of Thessalonica|De fide catolica]]'' of Emperor [[Theodosius I]].<ref>{{cite web |title=Theodosian Code XVI.i.2 |url=http://www.fordham.edu/halsall/source/theodcodeXVI.html |work=Medieval Sourcebook: Banning of Other Religions |first=Paul |last=Halsall |date=June 1997 |publisher=Fordham University |access-date=2006-11-23 |archive-date=27 February 2007 |archive-url=https://web.archive.org/web/20070227120555/http://www.fordham.edu/halsall/source/theodcodeXVI.html |url-status=dead }}</ref>