In the 1920s, Montparnasse took over from Montmartre as the stomping grounds of the capital's artistic colony, or at least of its avant-garde.
Montparnasse soon became totally obsolete. 
mnli hypothesis: Montparnasse soon became totally obsolete.  premise: In the 1920s, Montparnasse took over from Montmartre as the stomping grounds of the capital's artistic colony, or at least of its avant-garde.