quality:corruption, structural:expansion
Diocletian

In 284 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 Flavius Constantius (in the West). To adjust the economy, Diocletian made several tax reforms.

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. Diocletian did not use a disguised form of Republic, as the other emperors since Augustus had done. 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. 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. Diocletian abdicated in 305 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.