With a length of 11.7 km (7 mi), Line 3 crosses Paris from west to east completely on the Rive Droite, serving the residential areas of the 17th arrondissement, the Gare Saint-Lazare, important stores and shopping centres, the area around the Place de l'Opéra, as well as the east of the city, around République station.

In 2017, it carried 101.4 million riders, making it the tenth busiest line of the Métro network.

This masonry pit was 20 m (66 ft) and constructed fully so as to avoid any problems when building subsequent lines.

Since the work was situated at the water table, it required concrete pillars made by sinking caissons with compressed air.

In the area of the Place Gambetta, because of the instability of the subsoil, which consisted of waterlogged sand balls, made it necessary to drain the soil, a very delicate operation considering the number of buildings that could be destabilised.