Roman Empire

The Roman Empire (Latin: Imperium Romanum; Koinē Greek: Βασιλεία τῶν Ῥωμαίων, romanized: Basileía tōn Rhōmaíōn) is the successor state to the Roman Republic. The transition from republic to empire occurred in 727 AUC, when Gaius Octavius received the title of Augustus from the Senate. Centered on the Mediterranean Sea, at its height the empire stretched from the northern fringes of Britannia to the Persian Gulf. It's capital and largest city is Rome.

## History

*Main Article: History of the Roman Empire*

### Transition from Republic to Empire

Roman expansion began during the 3rd century AUC, after the foundation of the republic. However, it was not until the 6th century, that Rome began to expand outside of the Italian peninsula.  It could be argued that at that time Rome and its dominions already constituted an "empire", although its system of government continued to be that of a republic. During this period the Roman state did not function as a unified body, but rather a network of cities, each with a different degree of autonomy, all allied to or in submission to Rome.

Starting in the 7th century, Rome suffered a series of social conflicts, political conspiracies, and civil wars, while it continued to consolidate its influence beyond the Italian peninsula. These conflicts would ultimately result in the end of the Republic and the ascension of Augustus as the first Roman emperor.

### The Pax Augusta

The 200 years that began with Augustus's rule is traditionally regarded as the Pax Augusta ("Augustan Peace"). During this period, the cohesion of the empire was furthered by a degree of social stability and economic prosperity that Rome had never before experienced. Uprisings in the provinces were infrequent, but put down "mercilessly and swiftly" when they occurred. The success of Augustus in establishing principles of dynastic succession was limited by his outliving a number of talented potential heirs.

The Julio-Claudian dynasty lasted for four more emperors—Tiberius, Caligula, Claudius and Nero—before it yielded in 822 AUC to the strife-torn Year of Four Emperors, from which Vespasian emerged as victor. Vespasian became the founder of the brief Flavian dynasty, to be followed by the Nerva–Antonine dynasty which produced the "Five Good Emperors": Nerva, Trajan, Hadrian, Antoninus Pius and the philosophically-inclined Marcus Aurelius.

### The Crisis of the Tenth Century

*Main Article: Crisis of the Tenth Century*

After the Pax Augusta came the Severan dynasty. In 965 the Edict of Caracalla promulgated granted Roman citizenship to all free citizens of the Empire. However, despite this universal gesture, the Severan dynasty was marked by several revolts and disasters. Following the the assassination of Emperor Severus Alexander, the empire descended into the Crisis of the Tenth Century a time of invasions, social instability, economic difficulties, and plague. The Crisis would be brought to a close by the emperor Aurelian who reunited the empire and instituted reforms.

### The Pax Aurelia

*Main Article: Pax Aureliana*

The reunification and reforms of Aurelian ushered in a new roughly one hundred year long period of stability in the empire known as the Pax Aureliana (Peace of Aurelian). Succession in this period functioned under a system where in the Senate and Emperor would select a  Caesar, who would often be adopted by the emperor, to serve as the imperial heir. This system led to a string of strong emperors after Aurelian: Marcus Verus, Constantius Britannicus, Bassianus, and Constantine I who was the first Christian emperor. After Constantine the situation of the empire somewhat degraded, with the rise of Christianity causing an increasing amount of internal strife, and the end date of the Pax Aureliana is debated among historians, though most date it to the death of Emperor Germanus.

### The Barbarian Invasions and Decline

As a remedy for the growing conflict between religions, which was more and more taking a political center stage, Germanus instituted a system in which a Christian and non-Christian would serve as co-emperors, and Germanus appointed the pagan Messalla as his co-emperor. This system remained intact for 67 years, known as the Imperial Compromise or the Valeria-Constantinian dynasty, before Justin I became sole ruler of the empire again. During this time the period of Barbarian invasions, also sometimes called the Crisis of the Twelfth Century, also began, and the empire strained under the weight of the migrations as well as internal instability. The short lived Gaudentian dynasty saw the emperor Aetius largely stabilize the empire in the wake of these invasions, settling most of the tribes within the empire, as loyal foederati.

However most of his work stabilizing the empire was undone when his son and successor Gaudentius II was assassinated, plunging the empire into the brutal ten yearlong civil war known as the Anno Chao (Years of Chaos). The radical Christian Theodosius emerged victorious though the damage to the empire was great, former foederati had once more become hostile to Rome, and the empire was greatly decentralized as some governors ruled over territory more as hereditary monarchs or warlords than provincial governors. Theodosius established Antiochene Christianity as the official religion of the empire, persecuting all other faiths. Theodosius' successors, in the period known as the Pontificate because of the strong power of the church, lost large swaths of the empire to Barbarian kingdoms, small independent Roman rump states, and large secessionist empires such as the Southern Roman Empire and the Second Palmyrene Empire. Some of this territory wouldn't be recovered.

In 1255 the Emperor  Romanus was overthrown by his German Comes Domesticorum Diaco, who installed Vigilius (emperor) Vigilius as emperor. Romanus' overthrow began what is known as the German Tyranny, where a series of puppet emperors reigned while a succession of several German Comes Domesticorum held the real power essentially as military dictators of the Empire.