Emperor (Lat. imperator, commander), a title bestowed in the Roman republic on chief commanders of great armies, on consuls elect before entering upon their office, and often used by victorious troops to hail on the battle field a successful general. In later times it designated the highest authority in the state. Caesar, returning from his last campaign, after the victory of Munda (45 B. C), received it in this sense, but died soon after. Octavianus Augustus, after the battle of Actium (31 B. C), assumed this now regal title in preference to rex, and Rome became an empire. Augustus and his successors took in addition the name of Caesar, and both the title and the name (Kaiser) were afterward adopted by mon-archs of other states. When the rule of the Roman empire was divided, the name Caesar designated the adopted assistant of the emperor, who was himself honored by the title of Augustus. These titles disappeared in the West with the fall of Rome (476), but continued in the eastern or Byzantine empire for nearly ten centuries longer. During the crusades we find also a Nicaean and a Trapezun-tine empire in the East. But all these eastern states were swept away and replaced by the power of the Turks, whose sultans never officially adopted the title of the vanquished Christian monarchs.
This had been restored in the mean while in the West by Charlemagne, who received the imperial crown from the hands of Leo III. at Rome on Christmas day, 800, and was hailed by the people with shouts of "Life and victory to Carolus Augustus, the God-sent, pious, and great emperor of Rome, the bringer of peace." When the empire of this great Frankish monarch was divided by his grandsons, the title of emperor of Rome was given to the eldest of them, the king of Italy, and his descendants bore it until it was taken (962) by the mightier king of Germany, Otho I. And now began a long series of expeditions to Italy, undertaken by the German monarchs, in order to be crowned in Milan with the iron crown of Lombardy, and in Rome by the pope with that of the Roman empire; a series of struggles between the emperors, claiming the sovereignty of the Roman world according to their title, and the popes, claiming the same as successors of St. Peter; between the worldly and spiritual heads of the Christian nations. German bravery and Italian diplomacy were by turns victorious and vanquished; emperors were humiliated, popes were stripped of their dignity; Germany was distracted and Italy desolated. The reformation struck at the pope, and indirectly at the empire.
The German kings, who usually had been elected exclusively from Frankish or German houses, in earlier times by all, but later only by the greatest princes of Germany, who were hence called electors, gave up their Roman imperial pretensions, and were crowned in Germany as emperors of that country. At their coronation, celebrated in Aix-la-Chapelle, Augsburg, Ratisbon, or Frankfort, the emperors were obliged to sign an instrument, called capitulation, containing the conditions under which they were raised to their dignity. They lived in palatia set apart for their use (Pfal-zen), in later times in their hereditary dominions. The wars of the reformation broke the ancient forms and institutions; the imperial dignity became almost hereditary in the house of Austria; the other German states were made nearly independent; Prussia became a kingdom under Frederick I.; and the unity of Germany was virtually destroyed. The wars that followed the French revolution 'wrought still greater changes, and when Napoleon had assumed the imperial dignity (1804), and founded the Rhenish confederacy, Francis IT., who had proclaimed himself emperor of Austria in 1804 (as such Francis I.), in 1806 finally renounced the German imperial title, and what was once the Roman, now the German, empire expired.
Its restoration was during the revolutionary period of 1848-'9 the favorite idea of a party in the Frankfort parliament; but the refusal of the king of Prussia to accept the imperial crown made the scheme a failure. - Several other monarchies of Europe had taken the imperial title. Russia assumed it under Peter the Great (1721), and the assumption was in time acknowledged by all the states of Europe. The empire of the French, founded by Napoleon on the ruins of the republic, perished at Waterloo (1815), but was revived after two revolutions by the nephew of its founder (1852), and was succeeded by a republic, proclaimed Sept. 4, 1870. The empire of Germany was reestablished by the assumption of the title of emperor by King William of Prussia, Jan. 18, 1871. On the American continent several empires have been established, but most of them destroyed by revolutions. That of Mexico under Iturbide (1822) was ephemeral; under Maximilian it lasted from June 12, 1864, to June 19,1867. That of Brazil is governed constitutionally. That of Hayti, which was nominally constitutional, was overthrown in January, 1859, and replaced by a republic.
The Asiatic states of China, Japan, and Anam, and the African Fez and Morocco, are also often called empires.