Ancient Rome

==Empire – The Tetrarchy==
{{Main|Tetrarchy}}

===Diocletian===
[[File:DiocletianusFollis-transparent.png|thumb|A Roman [[follis]] depicting the profile of [[Diocletian]]]]
In 284&nbsp;AD, Diocletian was hailed as Imperator by the eastern army. Diocletian healed the empire from the crisis, by political and economic shifts. A new form of government was established: the [[Tetrarchy]]. The Empire was divided among four emperors, two in the West and two in the East. The first tetrarchs were Diocletian (in the East), [[Maximian]] (in the West), and two junior emperors, [[Galerius]] (in the East) and [[Constantius Chlorus|Flavius Constantius]] (in the West). To adjust the economy, Diocletian made several tax reforms.<ref>{{Citation |chapter-url=http://people.ucalgary.ca/~vandersp/Courses/texts/lactant/lactpers.html#VII |author=Lactantius |title=De Mortibus Persecutorum |chapter=VII}}</ref>

Diocletian expelled the Persians who plundered Syria and conquered some barbarian tribes with Maximian. He adopted many behaviours of Eastern monarchs. Anyone in the presence of the emperor had now to prostrate himself—a common act in the East, but never practised in Rome before.<ref>Joannes Zonaras, ''Epitome: From Diocletian to the death of Galerius''</ref> Diocletian did not use a disguised form of Republic, as the other emperors since [[Augustus]] had done.<ref>[http://www.roman-emperors.org/dioclet.htm Diocletian (284–305 AD)] by Ralph W. Mathisen. De Imperatoribus Romanis. 17 March 1997. Retrieved 20 March 2007.</ref> Between 290 and 330, half a dozen new capitals had been established by the members of the Tetrarchy, officially or not: Antioch, Nicomedia, Thessalonike, Sirmium, Milan, and Trier.{{Sfn|Ward-Perkins |1994}} Diocletian was also responsible for a significant Christian persecution. In 303 he and [[Galerius]] started the persecution and ordered the destruction of all the Christian churches and scripts and forbade Christian worship.<ref>{{Citation |chapter-url=http://people.ucalgary.ca/~vandersp/Courses/texts/lactant/lactpers.html#X |author=Lactantius |title=De Mortibus Persecutorum |chapter=X–XVI}}</ref> Diocletian abdicated in 305&nbsp;AD together with Maximian, thus, he was the first Roman emperor to resign. His reign ended the traditional form of imperial rule, the [[Principate]] (from [[princeps]]) and started the Tetrarchy.
[[File:Trier Konstantinbasilika BW 2017-06-16 14-07-56.jpg|thumb|The [[Aula Palatina]] of [[Trier]], Germany (then part of the [[Roman province]] of [[Gallia Belgica]]), a [[State church of the Roman Empire|Christian]] [[basilica]] built during the reign of [[Constantine I]] (r. 306–337 AD)]]

=== Constantine and Christianity ===
[[Constantine I|Constantine]] assumed the empire as a tetrarch in 306. He conducted many wars against the other tetrarchs. Firstly he defeated [[Maxentius]] in 312. In 313, he issued the [[Edict of Milan]], which granted liberty for Christians to profess their religion.<ref>{{Cite book |last=Gibbon |first=Edward |title=The History of the Decline and Fall of the Roman Empire |date=1906 |publisher=Fred de Fau and Co. |editor-last=Bury |editor-first=J.B. |language=en |chapter=Chapter XX}}</ref> Constantine was converted to Christianity, enforcing the Christian faith. He began the Christianization of the Empire and of Europe—a process concluded by the Catholic Church in the [[Middle Ages]]. He was defeated by the [[Franks]] and the [[Alamanni]] during 306–308. In 324 he defeated another tetrarch, [[Licinius]], and controlled all the empire, as it was before [[Diocletian]]. To celebrate his victories and Christianity's relevance, he rebuilt [[Byzantium]] and renamed it Nova Roma ("New Rome"); but the city soon gained the informal name of [[Constantinople]] ("City of Constantine").<ref>{{Cite book |last=Gibbon |first=Edward |title=The History of the Decline and Fall of the Roman Empire |date=1906 |publisher=Fred de Fau and Co. |editor-last=Bury |editor-first=J.B. |language=en |chapter=Chapter XVII |chapter-url=https://www.gutenberg.org/files/25717/25717-h/25717-h.htm#Blink182HCH0001 |chapter-format=Online version}}; [http://www.roman-emperors.org/conniei.htm Constantine I (306–337 AD)] by Hans A. Pohlsander. De Imperatoribus Romanis. 8 January 2004. Retrieved 20 March 2007.</ref>

The reign of [[Julian the Apostate|Julian]], who under the influence of his adviser [[Mardonius (philosopher)|Mardonius]] attempted to restore [[Religion in ancient Rome|Classical Roman]] and [[Hellenistic religion]], only briefly interrupted the succession of Christian emperors. Constantinople served as a new capital for the Empire. In fact, Rome had lost its central importance since the Crisis of the Third Century—[[Mediolanum]] was the western capital from 286 to 330, until the reign of [[Honorius (emperor)|Honorius]], when [[Ravenna]] was made capital, in the 5th century.<ref>[http://www.roman-emperors.org/honorius.htm Honorius (395–423 AD)] by Ralph W. Mathisen. De Imperatoribus Romanis. 2 June 1999. Retrieved 21 March 2007.</ref> Constantine's administrative and monetary reforms, that reunited the Empire under one emperor, and rebuilt the city of Byzantium, as Constantinopolis Nova Roma, changed the high period of the [[Classical antiquity|ancient world]].