Why did the Emperor Constatine decide to rebuild old port city of Byzantium in 4th century AD?

Emperor Constantine did not built the city of Byzantium. It was already a bustling city, dating back to the 7th century BC, when it was founded by Megarian colonists. He did, however, choose the site of Byzantium as the new capital of the Roman Empire in 330 AD, and renamed it Constantinople in his honour.