The Roman Empire
Classical Antiquity
Lift not my head from the bloody ground,
Bear not my body home,
For all the earth is Roman earth,
And I shall die in Rome."
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, trying to pass power to his (highly dysfunctional) family, though eventually emperors were chosen by the military, the Senate, or the imperial Praetorian Guard. Some emperors, such as Antoninus Pius or Marcus Aurelius, were wise and effective rulers. Others, such as Caligula, Elagabalus, or Commodus, were batshit crazy. Neverthless, for about two hundred years after Augustus, the Mediterranean world prospered under the Pax Romana.
After the reign of Emperor Commodus, however, Rome entered a period called the Crisis of the Third Century. Rebellions became frequent, coups became commonplace, and the leading cause of death among emperors was assassination. The empire was invaded by "barbarian" tribes across the Rhine and Danube frontiers and came into conflict with a renewed Persian Empire. The crisis was eventually ended by Emperor 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. 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. He called it "New Rome," but it became known as Constantinople. This city would survive as the Roman capital for over a thousand years.