Aurelius Victor

The Roman Empire was the post-Republican period of ancient Rome. As a polity, it included large territorial holdings around the Mediterranean Sea in Europe, North Africa, and Western Asia, and was ruled by emperors. From the accession of Caesar Augustus as the first Roman emperor to the military anarchy of the 3rd century, it was a Principate with Italia as the metropole of its provinces and the city of Rome as its sole capital. The Empire was later ruled by multiple emperors who shared control over the Western Roman Empire and the Eastern Roman Empire. The city of Rome remained the nominal capital of both parts until AD 476 when the imperial insignia were sent to Constantinople following the capture of the Western capital of Ravenna by the Germanic barbarians. The adoption of Christianity as the state church of the Roman Empire in AD 380 and the fall of the Western Roman Empire to Germanic kings conventionally marks the end of classical antiquity and the beginning of the Middle Ages. Because of these events, along with the gradual Hellenization of the Eastern Roman Empire, historians distinguish the medieval Roman Empire that remained in the Eastern provinces as the Byzantine Empire.

Caesar Augustus, also known as Octavian, was the first Roman emperor; he reigned from 27 BC until his death in AD 14. He is known for being the founder of the Roman Principate, which is the first phase of the Roman Empire, and is considered one of the greatest leaders in human history. The reign of Augustus initiated an imperial cult as well as an era associated with imperial peace, the Pax Romana or Pax Augusta. The Roman world was largely free from large-scale conflict for more than two centuries despite continuous wars of imperial expansion on the empire's frontiers and the year-long civil war known as the "Year of the Four Emperors" over the imperial succession.

Constantius II was Roman emperor from 337 to 361. His reign saw constant warfare on the borders against the Sasanian Empire and Germanic peoples, while internally the Roman Empire went through repeated civil wars, court intrigues, and usurpations. His religious policies inflamed domestic conflicts that would continue after his death.

Julian was Roman emperor from 361 to 363, as well as a notable philosopher and author in Greek. His rejection of Christianity, and his promotion of Neoplatonic Hellenism in its place, caused him to be remembered as Julian the Apostate in Christian tradition.

Pannonia Secunda was one of the provinces of the Roman Empire. It was formed in the year 296, during the reign of emperor Diocletian. The capital of the province was Sirmium. Pannonia Secunda included parts of present-day Serbia, Croatia, and Bosnia and Herzegovina.

The praefectus urbanus, also called praefectus urbi or urban prefect in English, was prefect of the city of Rome, and later also of Constantinople. The office originated under the Roman kings, continued during the Republic and Empire, and held high importance in late Antiquity. The office survived the collapse of the Western Roman Empire, and the last urban prefect of Rome, named Iohannes, is attested in 599. In the East, in Constantinople, the office survived until the 13th century.