Here is an old Paris postcard from around 1910, showing the Paris metro, the Boulevard Pasteur, the Avenue de Breteuil and the Invalides.
The card was printed by C.M. (Malcuit photo-editing house, located at 3 rue Bourdaloue. The Malcuit brothers signed their work under C.M. or E.M. labels).
The metro line going along the Boulevard Pasteur is currently line 6, but at the time it was line 5. The line was born in 1900 as line 2 sud or Circulaire sud and went from Etoile to Place d’Italie. In 1906, it was integrated to line 5 which connected Place d’Italie to Gare du Nord. It was many years later, in 1942, that it became line 6 (which has then kept until today the same stations layout), when the Etoile – Place d’Italie section of line 5 was transferred to the existing line 6, created in 1909 and going from Place d’Italie to Nation.
A 1939 map of the metro network shows the configuration of lines 5 and 6 at the time.
On the postcard, at the corner of Boulevard Pasteur and Avenue de Breteuil, we can see an advertising for LU or Lefèvre Utile, a biscuits manufacturer, creator of the famous Petit Beurre.