Depending on where you draw the line, Paris has either roughly the same population as London — ten million within the M25 or the “Grand Paris Region,” give or take — or less than a quarter, with only two million people living within the Périphérique, the 1960s motorway that encircles the historic city.

Whereas, thanks to the Luftwaffe and the London County Council, most of London’s working class lives in London proper, with everywhere except perhaps Belgravia and Mayfair having large council estates, in “Paris proper” only the north and east have anything like the same social mix. Even the transport system feels segregated — the historic Métro for “Paris,” the futuristic but shabby and foul-smelling RER for the “Paris region.” So every time I’ve visited, I’ve taken an RER journey out to the banlieues, the suburbs, to spend some time in areas where you can see something a bit more exciting than endless six-story limestone blocks of flats built under Napoleon III.

This is Paris’s historic “Red Belt,” a girdle of concrete where most of the Parisian working class lives, where the Parti Communiste Français built its strongest base, and where, unlike much of formerly industrial France, the Left, whether the socialists, the communists, or Mélenchon’s various vehicles, still dominates the political scene. As with London, this place has voted consistently for the Left for a century, yet it is too multicultural and diverse to be considered anyone’s “heartland.” It’s a fascinating and thrilling place, though it can be bleak — and if the French capital has a future, it is being made there.