Final answer:
Emperor Constantine the Great moved the capital of the Roman Empire to Byzantium in 330, renaming it Constantinople, which is known today as Istanbul.
Step-by-step explanation:
In 330, Emperor Constantine the Great moved the capital of the Roman Empire to the ancient Greek city of Byzantium, which he renamed Constantinople. The city's original name was Byzantion, and it is known as Istanbul today.
Constantinople was strategically located at the junction of Europe and Anatolia, controlling the Bosphorus Strait and serving as a key trade route between Asia and Europe, thus becoming a center of wealth, power, and Christian influence within the Empire. Over time, this city became one of the most important cities of the late antique and medieval periods until the fall of the Byzantine Empire in 1453 CE when it was conquered by the Ottoman Turks.