Basic Supplies: Food and Water
The accessibility of such huge quantities of both clean water and food was critical in allowing Rome to grow to and sustain over 1,000,000 people by 110 AD. It was also a huge factor in Rome's decline in the fourth and fifth centuries.
WATER. Roman developed a system of aqueducts that brought into the city more clean running water per day than New York City was receiving in the 1980s. It cannot be overstated the importance of the aqueducts to the ability of Rome to grow so large in early times.
"In height of empire, Rome had nine aqueducts which fed 39 monumental fountains and 591 public basins, not counting the water supplied to the Imperial & wealthy private households. Each of the major fountains was connected to two different aqueducts, in case one was shut down for service. " (James, 1998)
FOOD. After conquering of Sicily and northern Africa, the Roman Empire
used these lands as the main grain sources for the city of Rome. The surrounding countryside outside of Rome was not large enough to sustain a city of over 1,000,000 people. And the amount of wealth streaming into the city from conquests led to the countryside being used as recreational
estates for the wealthy of Rome. Farming was done only for perishable
goods like olives, fruit, and vegetables. (Trashopolis, 2011)
The fact that both of these critical elements were available only because the city was the center of the Roman Empire made the Romans within the city very vulnerable. When Rome lost the North African territory in the 400s, the city lost a food supply that was never possible to sustain with the surrounding hinterlands of the city. Likewise, when the Goths finally approached Rome in 410 AD, they simply destroyed the aqueducts just outside the city walls and waited for the residents to suffer. They then entered the city with little-to-no resistance. (Dark Ages, 2009)