Which aspect of Roman city life contributed to the spread of disease?

Historical sources suggest that Roman soldiers returning from campaign in Mesopotamia spread the disease, which lasted from 165-180 AD. Based on the written observations of fever, diarrhea, and boils by the Greek physician Galen, historians infer that smallpox caused the plague.

Explanation:

answer; ///i do believe that the correct answer is (d); ///athens had a small population;

it affected it because the kingdoms (with trade) slowly got richer and richer.