Which emperor founded Constantinople as a new imperial capital in 330?

Constantine the Great founded Constantinople as a new imperial capital in 330. He selected the site of Byzantium, an older Greek settlement on the Bosporus, and expanded it into a city intended to rival Rome.

The location offered major strategic advantages. Constantinople stood between Europe and Asia, near the Danube and eastern frontiers, while its harbors and position along trade routes supported commerce and military movement. Constantine ceremonially dedicated the city on 11 May 330, presenting it as a new Roman center rather than simply a provincial capital.

The city was also known as New Rome, although Constantinople became the more familiar name. After the Roman Empire was permanently divided in 395, it served as the capital of the Eastern Roman Empire, later called the Byzantine Empire. Theodosius I did not found it, Justinian I rebuilt parts of it after the Nika riots, and Diocletian ruled before its foundation.