La Spezia-Rimini Line

The La Spezia–Rimini Line, in the linguistics of the Romance languages, is a line that demarcates a number of important isoglosses that distinguish Romance languages south and east of the line from Romance languages north and west of it. Romance languages on the eastern half of it include Italian and the Vlach languages (Romanian, Aromanian, Megleno-Romanian, Istro-Romanian), while Spanish, French, Catalan, Portuguese as well as Northern Italian languages are representatives of the western group.
 
http://en.wikipedia.org/wiki/La_Spezia-Rimini_Line