Paris Métro Line 12

Paris Métro Line 12 (opened as Line A; French: Ligne 12 du métro de Paris) is one of the sixteen lines of the Paris Métro. It links Issy-les-Moulineaux, a suburban town southwest of Paris, to Aubervilliers, in the north. With around 54 million passengers per year, Line 12 was the twelfth busiest line of the network in 2021. It has several major stops, such as Madeleine, Concorde, Porte de Versailles and two national railway stations, Gare Montparnasse and Gare Saint-Lazare. The service runs every day of the week, and the line uses MF 67 series trains, the network's standard since the early 1970s.

Line 12 was founded as Line A by the Nord-Sud Company, who also built Line 13. It was built between 1905 and 1910, to connect the districts of Montparnasse, in the south, and Montmartre, in the north. The first trip, from Porte de Versailles to Notre-Dame-de-Lorette, was on 5 November 1910. The line was the second to be built on the north–south axis of the city, in competition with Line 4 of the Compagnie du chemin de fer métropolitain de Paris (CMP; Paris Metropolitan Railway Company). It was extended southward bit by bit until 1934 when it reached Mairie d'Issy in the south. Tunnelling to the northern terminus at the Porte de la Chapelle on the perimeter of Paris had been completed in 1916. In 1930, the CMP bought the Nord-Sud company and Line A was integrated into the new, unified network as Line 12. In 1949, the CMP was itself merged into the RATP, Paris's public transport company. They operate the line today and have plans to extend it south as far as the town of Issy-les-Moulineaux and north to La Plaine in Saint-Denis.

The line was built using cut-and-cover excavation techniques. Since this method cannot be used under buildings, the route follows the streets above. It remains unchanged today and many original design features, such as the Nord-Sud company's refined ceramic decor, remain in the stations. Some stations are decorated thematically: Assemblée Nationale has murals explaining the intricacies of the lower house of the French Parliament, while the tiling at Concorde represents an extract from the Declaration of the Rights of Man and of the Citizen (1789).