> Ancient Rome was full of 5-7 story apartment buildings and had a population of around a million. Higher density than a whole lot of modern cities, the vast m

> Ancient Rome was full of 5-7 story apartment buildings and had a population of around a million. Higher density than a whole lot of modern cities, the vast majority of which are not seas of skyscrapers. This isn't really true - the Aurelian walls were about 14 square kilometers, but a significant portion of the city's 1 million people lived outside the Aurelian walls. We don't have a good sense of how many people lived within the Aurelian walls, but number that's often cited (1 million people/14 square km = 70,000 people/square km, 2.5 times the most dense city in the world today) is not actually representative of what ancient Rome looked like at any period in history.