So well, the title explains my question, I'm from Milan and in school they also taught us this, but they never explained why. I don't think the city and its vicinity was much better than other European cities, and it is not on the top of a mountain or something similar, but at the very centre of a flat land. So what could be the causes? Thanks in advance.
While more can be added, This answer by u/snackburros would be of interest for you, giving details on the quarantine Milan enacted to isolate the sick outside the city walls.