In France - a country of Catholic tradition - showing your wealth is very badly considered, if not a sin! Therefore, if you happen to be richer than your neighbour, you may want to hide it... We even have a saying that sums it up "Pour vivre heureux, vivons cachés" (If you want to be happy, keep your head down) Therefore, it's not very surprising that in Paris, the chicest places to live are generally concealed from the view of everybody... Hence this Square du Croizic, a sort of "gated community" in the heart of Montparnasse where no cars are allowed and where all buildings were built according to the Haussmann rules. There are many many places like this in Paris in all arrondissement, even in Montmartre. Needless to say they're pretty expensive!