Culture of ancient Rome
The Roman Empire, at its height (c. 117 CE), was the most extensive political and social structure in western civilization. By 285 CE the empire had grown too vast to be ruled from the central government at Rome and so was divided by Emperor Diocletian into a Western and an Eastern Empire. The Roman Empire began when Augustus Caesar became the first emperor of Rome (31 BCE) and ended, in the west, when the last Roman emperor, Romulus Augustulus, was deposed by the Germanic King Odoacer (476 CE). In the east, it continued as the Byzantine Empire until the death of Constantine XI and the fall of Constantinople to the Ottoman Turks in 1453 CE. The influence of the Roman Empire on western civilization was profound in its lasting contributions to virtually every aspect of western culture.
Emperor
From the time of Otto the Great onward, much of the former Carolingian kingdom of Eastern Francia became the Holy Roman Empire. The prince-electors elected one of their peers as King of the Romans and King of Italy before being crowned by the Pope. The Emperor could also pursue the election of his heir (usually a son) as King, who would then succeed him after his death. This junior King then bore the title of Roman King (King of the Romans). Although technically already ruling, after the election he would be crowned as emperor by the Pope. The last emperor to be crowned by the pope was Charles V; all emperors after him were technically "emperors-elect", but were universally referred to as "Emperor".