The necessity of fighting off invading groups was one aspect of the Roman Empire that continued into the Byzantine Empire.
The Byzantine Empire, a very powerful and vast civilisation, emerged after the Roman Empire during Late Antiquity and the Middle Ages. Constantinople became its capital.
The Roman Empire marked the post-Republican period of ancient Rome. During this time period they held territories along the Mediterranean sea. The rulers of the Empire were known as emperors and many of them ruled during its existence.