Which empire was ruled from Constantinople after 330 AD?

The Byzantine Empire was governed from Constantinople, which Constantine founded in 330 on the site of the older Greek colony of Byzantium and named after himself. It was a superb choice of ground: a peninsula guarded on one side by a deep natural harbour, controlling the strait between Europe and Asia and the sea route between the Mediterranean and the Black Sea, and defensible by land behind a single line of walls. Byzantine is a later label. Its people called themselves Romans and considered their state the continuation of the Roman Empire, which it was; when the western provinces fell in the fifth century, the eastern half simply carried on for another thousand years, Greek-speaking, Orthodox in religion, and governed under a codified Roman law that Justinian had reorganised. Constantinople finally fell to Ottoman forces in 1453 after artillery made its walls, long thought impregnable, obsolete.

The Hagia Sophia, built under Justinian, stood as the largest domed interior in the world for centuries.