Ancient Rome was 8-times more densely populated than what modern city?
It is estimated that ancient Rome's inhabitant count was proportionally higher than modern-day Rome. Insulae (apartments) were multistoried, and roads so narrow that neighbors on opposite sides could lean over their balconies and shake hands. Frequent traffic related deaths and injuries led to strict conveyance laws. To the chagrin of merchants, carts and wagons could only use the streets after dark. (See First Century Life: Night Traffic)