The Paris Métro runs mostly underground; surface sections include sections on viaduct in Paris (Lines 1, 2, 5 and 6) and at the surface in the suburbs (Lines 1, 5, 8 and 13). In most cases both tracks are laid in a single tunnel. Almost all lines follow roads, having been built by the cut-and-cover method near the surface (the earliest by hand). Line 1 follows the straight course of the Champs-Elysées and on other lines some stations (Liège, Commerce) have platforms that do not align: the street above is too narrow to fit both platforms opposite each other. Many lines have very sharp curves. The specifications established in 1900 required a very low minimum curve radius by railway standards, but even this was often not fully respected, for example near Bastille and Notre Dame de Lorette. Parts of the network are built at depth, in particular a section of Line 12 under Montmartre, the sections under the Seine, and all of Line 14.