The Roman Empire was the post-Republican period of the ancient Roman civilisation that had been characterised by a dictatorial form of government and large territorial resources around the Mediterranean in Europe, Africa, and Asia.
Before the Empire was established, the 500 year old Roman Republic reigned and was weakened through a series of civil wars and because of several other events this caused the transition from a Republic to an Empire and included Julius Caesar's appointment as eternal ruler in 44 BC; the Battle of Actium in 31 BC and in 27 BC the Roman Senate granted the honorific Augustus to Octavian.
The Empire’s first two centuries were a period of exceptional prosperity, growth and stability known as the Pax Romana ( Roman Peace ). It was during the reign of Trajan (98–117 AD) that it achieved its greatest expansion and in the 3rd century suffered a crisis that threatened its whole existence but was reunited and stabilised under Emperors Aurelian and Diocletian. In the 4th century when the Christians took power a system of dual rule developed in the Latin West and Greek East. When the Latin West’s central government collapsed in the 5th century the Greek East continued and became known as the Byzantine Empire.
Due to the Empire’s vastness and its continued existence, the Roman culture and institutions had a deep and lasting influence on the development of law, philosophy, architecture, religion, and language along with the forms of government within the territory it ruled, especially Europe and Europe’s expansion throughout the modern world.