The capital of the Roman Empire in 14 CE had over 750,000 inhabitants, which constituted a tenth of the entire population of Italy. The population of Rome grew to over a million by the end of the 2nd century CE. This number was achieved by western cities only in the 19th century.
Other major cities of the Empire, such as Antioch, Alexandria, and late Carthage, had a population of several hundred thousand inhabitants.
In turn, the Roman Empire at its peak in 117 CE during the reign of Emperor Trajan was about 5 million square kilometres. The state was inhabited by about 70 million people, which was 21% of the world’s population.