I just watched an interesting video that recreates Rome as it probably was circa 320 AD. At that point, Rome’s population was somewhere between one and two million people, the largest city in Europe until 19th century London. Constantine was Emperor and a few years later, he would move his capital to Constantinople. A century and a half later, the final emperors would die.
I’ve only visited Rome once, when I was ten years old. I’m long overdue for another visit.