The
Roman Empire (;
Ancient and
Medieval Greek: Βασιλεία τῶν Ῥωμαίων,
tr. ) was the post-
Roman Republic period of the
ancient Roman civilization, characterized by government headed by
emperors and large territorial holdings around the
Mediterranean Sea in Europe, Africa and Asia. The city of
Rome extended and between c. 100 BC- 400 AD was the
largest city in the world, whereas
Constantinople (New Rome) retained the first position around 500 AD, whilst the Empire's populace grew into an estimated 50 to 90 million inhabitants (roughly 20% of the world's population at the time). The 500-year-old
republic which preceded it was severely destabilized in a series of
civil wars and political conflict, during which
Julius Caesar was appointed as perpetual
dictator and then assassinated in 44 BC. Civil wars and
executions continued, culminating in the victory of
Octavian, Caesar's adopted son, over
Mark Antony and
Cleopatra at the
Battle of Actium in 31 BC and the annexation of
Egypt. Octavian's power was now unassailable and in 27 BC the Roman Senate formally granted him
overarching power and the new title
Augustus, effectively marking the end of the
Roman Republic.