How was rome like major cities today?

Rome reached its peak in inhabitants by 100 aD. Numbers vary, but it is fine to suppose something like 1,5 million people. Most of the city were slums called "insulae", buildings up to seven stories high belonging to the elite and rented to common people. One "apartment" in an insulae was normally just one room (10 m2) where up to 10 could sleep, with no water.