The early Roman Empire

The Roman Empire stretched across three continents: Europe, North Africa and West Asia. Historians divide its story into the early empire (to the third century) and late antiquity (fourth to seventh centuries).

Sources for Roman history fall into three groups:

• Texts: histories of the period written year by year (annals), letters, speeches, sermons and laws.
• Documents: inscriptions carved on stone, and papyri, writings on papyrus, a reed-like plant that grew along the Nile and was made into a writing material. Thousands of contracts, accounts and letters survive this way, especially in Egypt.
• Material remains: buildings, monuments, coins, pottery, mosaics and even whole landscapes, studied through archaeology and aerial photography.

Two superpowers. From the first century BCE to the seventh century CE, most of Europe, North Africa and West Asia was divided between Rome and Iran. They were rivals and often at war; a narrow strip along the river Euphrates separated them. The Mediterranean Sea was the heart of Rome's empire, with the Atlantic to the west, the rivers Rhine and Danube to the north and the Sahara to the south.

From republic to empire. In 27 BCE Augustus, the adopted son of Julius Caesar, became the first emperor. The system he founded is called the Principate: the emperor was officially only the 'leading citizen' (princeps), not an absolute ruler, out of respect for the Senate, though in practice he held supreme power.

Power was shared among three players:

• The emperor.
• The Senate: a body of wealthy families, mostly landowners of Italian origin, which had controlled Rome in the days of the republic. Membership was for life and depended more on wealth and birth than on merit. Much Roman history was written by senators, so emperors who angered them were often remembered badly.
• The army: unlike the conscripted army of Iran, Rome's was a paid, professional army of about 600,000 men, who served for at least 25 years. It was the largest single organised body in the empire and could make or unmake emperors; soldiers often agitated for better pay and conditions.

Succession was based on family descent, natural or adopted: Augustus's adopted son Tiberius followed him. There was surprisingly little civil war; the main exception was 69 CE, when four emperors held power in a single year. Apart from Trajan's short-lived conquest beyond the Euphrates (113 to 117 CE), abandoned by his successors, early emperors mostly defended what they had rather than seeking new lands.

Ruling through cities. The empire held about 60 million people, and the emperor could not govern them all directly. Outside Italy, which was not taxed as a province, territory was organised into provinces around great cities such as Carthage, Alexandria and Antioch. Each city had magistrates and a council, and the local upper classes worked with the Roman state to run the city and collect taxes from the surrounding countryside. Cities enjoyed better food supplies than villages, and offered public baths and shows (spectacula).

Over the second and third centuries, more and more provincials rose to power as governors, officers and even senators. Italians lost their hold on the Senate, and by the third century most senators came from the provinces. The emperor Gallienus went further and excluded senators from military command altogether, to stop them taking control of the army.