> I recently read that Marseilles is a prison of rival drug cartels.
You've read rubbish. Marseille has gang issues in some neighborhood but it's not a « prison ». It's certainly paying the price for poor urbanism in the 50s, though. But things are generally improving.
How many major French cities are strangling themselves? How many are not?
https://www.bbc.com/news/world-europe-58395124