Caesar established himself as dictator for life. His assassination led to a second Triumvirate among Octavian (Caesar's grandnephew and heir), Mark Antony and Lepidus, and to another civil war between Octavian and Antony. Empire In 27 BC, Octavian became princeps civitatis and took the title of Augustus, founding the principate, a diarchy between the princeps and the senate. During the reign of Nero, two thirds of the city was ruined after the Great Fire of Rome, and the persecution of Christians commenced. Rome was established as a de facto empire, which reached its greatest expansion in the second century under the Emperor Trajan. Rome was confirmed as caput Mundi, i.e. the capital of the known world, an expression which had already been used in the Republican period. During its first two centuries, the empire was ruled by emperors of the Julio-Claudian, Flavian (who also built an eponymous amphitheatre, known as the Colosseum), and Antonine dynasties. This time was also characterised by the spread of the Christian religion, preached by Jesus Christ in Judea in the first half of the first century (under Tiberius) and popularised by his apostles through the empire and beyond. The Antonine age is considered the zenith of the Empire, whose territory ranged from the Atlantic Ocean to the Euphrates and from Britain to Egypt. After the end of the Severan Dynasty in 235, the Empire entered into a 50-year period known as the Crisis of the Third Century during which there were numerous putsches by generals, who sought to secure the region of the empire they were entrusted with due to the weakness of central authority in Rome. There was the so-called Gallic Empire from 260 to 274 and the revolts of Zenobia and her father from the mid-260s which sought to fend off Persian incursions. Some regions – Britain, Spain, and North Africa – were hardly affected. Instability caused economic deterioration, and there was a rapid rise in inflation as the government debased the currency in order to meet expenses. The Germanic tribes along the Rhine and north of the Balkans made serious, uncoordinated incursions from the 250s–280s that were more like giant raiding parties rather than attempts to settle. The Persian Empire invaded from the east several times during the 230s to 260s but were eventually defeated. Emperor Diocletian (284) undertook the restoration of the State. He ended the Principate and introduced the Tetrarchy