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.