a monarchical title. In ancient Rome the word imperium initially referred to the supreme power (military, juridical, and administrative) of the highest magistrates, including consuls, praetors, and dictators. From the period of Augustus and his successors the title of emperor in the Roman Empire took on a monarchical character. Beginning with the reign of Diocletian, the Roman Empire was ruled by two emperors with the title of Augustus; their two co-rulers held the title of caesar. With the fall of the Western Roman Empire (476) the title of emperor was retained in the East, in Byzantium; in the West it was restored by Charlemagne (800) and later by the German king Otto I (from 962, the emperor of the Holy Roman Empire). Subsequently the title was adopted by the monarchs of certain other states, including the Russian emperor, beginning in 1721, and the Austrian emperor, from 1804. In European literature the term “emperor” is applied to the monarchs of a number of non-European states, such as the Chinese emperor (until 1911) and the Japanese emperor.