Out of every city that survived the Last War and the Apocalypse, Rome was possibly the oldest. Perhaps New Athens existed longer, but before the Apocalypse, people mostly abandoned it.
In comparison, Rome's population always remained high. From the period of its founding, throughout the height of its republic and empire, into the future as the center of the world's largest religion, and at the end, as a tourist destination.
Rome's reputation and history remained intact, as far as everyone knew. Its population was between 25-30 million, its walls stretched high, and its people were loyal to the bitter end.
After seizing the area, the Federal Alliance disregarded the people's input in decision-making. This caused a serious discord in the populace, and Adam's propaganda only widened it.