The Roman Empire (Latin: Imperium Romanum) was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings around the Mediterranean in Europe, Africa, and Asia. The 500-year-old Roman Republic, which preceded it, had been destabilized through a series of civil wars. Several events marked the transition from Republic to Empire, including Julius Caesar's appointment as perpetual dictator (44 BC); the Battle of Actium (2 September 31 BC); and the granting of the honorific Augustus to Octavian by the Roman Senate (16 January 27 BC).
The first two centuries of the Empire were a period of unprecedented stability and prosperity known as the Pax Romana ("Roman Peace"). It reached its greatest expanse during the reign of Trajan (98–117 AD). In the 3rd century, the Empire underwent a crisis that threatened its existence, but was reunified and stabilized under the emperors Aurelian and Diocletian. Christians rose to power in the 4th century, during which time a system of dual rule was developed in the Latin West and Greek East. After the collapse of central government in the West in the 5th century, the eastern half continued as what would later be known as the Byzantine Empire.
Rome (//; Italian: Roma pronounced [ˈroːma] ( listen); Latin: Rōma) is a city and special comune (named "Roma Capitale") in Italy. Rome is the capital of Italy and also of the homonymous province and of the region of Lazio. With 2.8 million residents in 1,285.3 km2 (496.3 sq mi), it is also the country's largest and most populated comune and fifth-most populous city in the European Union by population within city limits. Between 3.2 and 3.8 million people live in the Rome urban and metropolitan area. The city is located in the central-western portion of the Italian Peninsula, on the Tiber within the Lazio region of Italy. Rome is referred to as "The Eternal City", a notion expressed by ancient Roman poets and writers.