Final answer:
The capital of the Eastern Roman Empire, originally named Constantinople, was changed to Istanbul in 1450 after being conquered by the Ottoman Turks.
Step-by-step explanation:
When the Roman Empire was split, the Eastern Roman Empire, also known as the Byzantine Empire, had its capital in Constantinople. In 1450, after the conquering of the city by the powerful Ottoman Turks, the name of the Eastern Roman Empire's capital was changed to Istanbul. This marked the conclusion of the Byzantine Empire, with a transition to Ottoman control and the start of a new chapter in the city's history.