The Roman Republic became the Roman Empire in 27 BC when Julius Caesar’s adopted son, best known as Augustus, became the ruler of Rome. Augustus established an autocratic form of government, where he was the sole ruler and made all important decisions. Although we refer to him as Rome’s first emperor, Augustus never took the title of king or emperor, nor did his successors; they preferred to call themselves princeps, first citizen, or primus inter pares, first among peers. This choice of title maintained the appearance of limited power that had been so important under the Republic.
Augustus established a form of government known as a principate, which combined some elements from the republic with the traditional powers of a monarchy. The Senate still functioned, though Augustus, as princeps, or first citizen, remained in control of the government. Under Augustus, Rome began to prosper once again, and the emperor came to be looked upon as a god. Thereafter, all good emperors were worshiped as gods after death. Among the beloved rulers of Rome were Trajan (reigned 98–117), Hadrian (117–138), Antoninus Pius (138–161), and Marcus Aurelius (161–180). Decadent, cruel men also rose to power: Caligula (37–41) and Nero (54–68) were so loathed that their reigns were struck from the official Roman records.
It was during the rule of Tiberius (14–37) that Jesus Christ was crucified. Thereafter, Christians were tolerated at best—but often tortured or killed—until the reign of Constantine I (312–337). In 313 an edict of toleration for all religions was issued, and from about 320 Christianity was favoured by the Roman state rather than persecuted by it. But the empire was dying. The last of Constantine’s line, Theodosius I (379–395), was the last emperor to rule over a unified Roman Empire. The Western Empire, suffering from repeated invasions and the flight of the peasants into the cities, had grown weak compared with the East, where spices and other exports virtually guaranteed wealth and stability. When Theodosius died, in 395, Rome split into Eastern and Western empires.
During the later republic and most of the empire, Rome was the dominant power in the entire Mediterranean basin, most of western Europe, and large areas of northern Africa. The Romans possessed a powerful army and were gifted in the applied arts of law, government, city planning, and statecraft, but they also acknowledged and adopted contributions of other ancient peoples—most notably, those of the Greeks, much of whose culture was thereby preserved.
The Roman Empire was distinguished not only for its outstanding army—the foundation upon which the whole empire rested—but also for its accomplishments in intellectual endeavours. Roman law, for example, was a considered and complex body of precedents and comments, which were all finally codified in the 6th century (see Justinian, Code of). Rome’s roads were without match in the ancient world, designed for comparatively fast transportation and adapted to a wide variety of functions: commerce, agriculture, mail delivery, pedestrian traffic, and military movements. Roman city planners achieved unprecedented standards of hygiene with their plumbing, sewage disposal, dams, and aqueducts. Roman architecture, though often imitative of Greek styles, was boldly planned and lavishly executed. Triumphal arches commemorated important state occasions, and the famous Roman baths were built to stir the senses as well as to cleanse the body.
Finally, Latin, the language of the Romans, became the medium for a significant body of original works in Western civilization. Cicero’s speeches, the histories of Livy and Tacitus, Terence’s drama, and above all the poetry of Virgil are all part of the legacy of Rome.