<P> Construction began on November 1898 . The first line, Porte Maillot--Porte de Vincennes, was inaugurated on 19 July 1900 during the Paris World's Fair . Entrances to stations were designed in Art Nouveau style by Hector Guimard . Eighty - six of his entrances are still in existence . </P> <P> Bienvenüe's project consisted of 10 lines, which correspond to today's Lines 1 to 9 . Construction was so intense that by 1920, despite a few changes from schedule, most lines had been completed . The shield method of construction was rejected in favor of the cut - and - cover method in order to speed up work . Bienvenüe, a highly regarded engineer, designed a special procedure of building the tunnels to allow the swift repaving of roads, and is credited with a largely swift and relatively uneventful construction through the difficult and heterogeneous soils and rocks . </P> <P> Lines 1 and 4 were conceived as central east - west and north - south lines . Two lines, ligne 2 Nord (line 2 North) and ligne 2 Sud (line 2 South), were also planned but line 2 South was merged with line 5 in 1906 . Line 3 was an additional east - west line to the north of line 1 and line 5 an additional north - south line to the east of line 4 . Line 6 would run from Nation to Place d'Italie . Lines 7, 8 and 9 would connect commercial and office districts around the Opéra to residential areas in the north - east and the south - west . Bienvenüe also planned a circular line, the ligne circulaire intérieure, to connect the six main - line stations . A section opened in 1923 between Invalides and the Boulevard Saint - Germain before the plan was abandoned . </P> <P> On 31 January 1904, a second concession was granted to the Société du chemin de fer électrique souterrain Nord - Sud de Paris (Paris North - South underground electrical railway company), abbreviated to the Nord - Sud (North - South) company . It was responsible for building three proposed lines: </P>

Where does the line go on 6 and 9