The Roman Empire

Over the next four hundred years, the Roman Empire continued to expand and consolidate its political and cultural hold over the Western world, until it stretched from Scotland to Persia. Conquered peoples were generally granted Roman citizenship and largely adopted the Roman culture as their own.

Augustus took care to make sure Rome still looked like a republic. The Senate continued to meet and public officials continued to be elected, but in reality, Augustus and his successor emperors held all the real power. Even so, Augustus only called himself the princeps, or "first citizen" (AKA totally not a king) and so the early imperial period is called the Principate.

Augustus reigned as emperor for 40 years. Some of his successors, such as Antoninus Pius and Marcus Aurelius, were wise and effective rulers. Others, such as Nero and Caligula, were vespertilio cacas rabidus. For about two hundred years after Augustus, the Mediterranean world prospered under the Pax Romana.

Eventually, however, Rome entered the Crisis of the Third Century, when rebellions became frequent, coups became commonplace, and the leading cause of death among emperors was assassination.

The crisis was ended by Diocletian, who made a number of changes with very long-lasting consequences. He dropped all pretense of republicanism and styled himself as a divine figure, adopting the title dominus or "lord." This second imperial period is therefore called the Dominate. The other important thing Diocletian did was create the Tetrarchy: he split the Empire into two halves, East and West. Each half had a senior emperor called the Augustus and a junior emperor called the Caesar. Diocletian thought this would create a stable pattern of succession, but in reality, he had just created an imperial playoff bracket.

A series of civil wars in which the members of the Tetrarchy eliminated each other left Constantine the Great in sole control of the Empire by 324 AD. He moved the Empire's capital from Rome to a small Greek city called Byzantium, which he renamed Constantinople.