Conversion, which commenced in 2007 and was completed in 2011, included new rolling stock (MP 05) and laying of platform edge doors in all stations.

The deterioration of traffic conditions in Paris, the example of foreign capitals and the approach of the 1900 Universal Exhibition convinced the authorities to start construction of the metro.

After the adoption by the municipal council on 20 April 1896 of the network project of Fulgence Bienvenüe and Edmond Huet, the "metropolitan railway" was declared a public utility by a law that became effective 30 March 1898.

Under an agreement of 27 January 1898 between the City and the Compagnie générale de traction, the network concessionaire, the company agreed to put the first three lines into service within eight years following the declaration of public utility.

[4] Work on line 1 began on 4 October 1898, as part of an agreement between the Paris administration and the Compagnie du chemin de fer métropolitain de Paris (CMP), which stipulated that the city would build the network infrastructure (tunnels, stations), with the concessionaire building the superstructure (tracks and access to stations).

The work on the line itself was carried out in record time: it lasted twenty months and was led by Fulgence Bienvenüe, a bridges and roads engineer, and financed by the city of Paris.

Eleven shields (a type of tunnel boring machine) were built for this work and installed under the roadways, with which approximately 2,500 m (8,200 ft) of tunnel were dug, including more than 1,500 m (4,900 ft) by the three Champigneul shields which dug from the Place de la Nation (in both directions) and that of the Porte Maillot.

The external entrance canopies (or edicules) were designed by the emblematic architect of art nouveau, Hector Guimard.

This plant supplied three-phase current at 5,000 volts 25 hertz, with its eighteen boilers with a heating surface of 244 m2 (2,630 sq ft) and its three 1,500 kW generator sets.

Before the Bercy plant was commissioned, electricity was supplied by the companies Le Triphasé (Asnières-sur-Seine) and the Compagnie générale de traction (Moulineaux).

Their introduction on the line was possible thanks to the slight relocation of Bastille station with curves of a larger radius allowing the passage of longer cars.

Nevertheless, the continuous increase in traffic highlighted the lack of capacity of the rolling stock: a new class of trains appeared during the 1920s, with even longer cars, 13.6 m (45 ft) long, and engines with "small boxes", leaving more space for passengers.

The extension to the Pont de Neuilly faced several difficulties: the terminal loop at Porte Maillot station had been built in 1900 at a shallow depth, at approximately the same level as the Petite Ceinture line.

It was therefore essential to reroute the line at the start of the return loop in order to lower the tunnel below the Petite Ceinture and to build a new Porte Maillot station.

The latter, with only two tracks, was designed as a temporary terminus, because it was then planned to extend the line to La Défense with an under-river crossing of the Seine.

[8] During the Second World War, and for the next two decades, Line 1, the busiest on the network, saw its ridership increase to the point of reaching significant overloads (up to 135% of its capacity), which degraded operation and transport conditions.

The SDAURP (Schéma directeur d'aménagement et d'urbanisme de la région parisienne, "Master plan for development and urban planning of the Paris region"), published in 1965 under the leadership of Prefect Paul Delouvrier, provided for the creation of a large-gauge regional rail transport network on the scale of the urban area.

This highly ambitious plan, already outlined in the 1920s, provided for the priority creation of a major east-west axis, to support regional growth, serve the new business district of La Défense and relieve some of the traffic on metro Line 1 and Gare Saint-Lazare, then the busiest in France.

Then, finally, it was the extension to Noisy-le-Grand – Mont d'Est and the opening of the central Auber – Nation section that completed the RER A line on 9 December 1977 after five more years of monumental works in the heart of Paris.

The bridge itself was widened by the construction of new cantilevered sidewalks over the Seine, in order to free up sufficient space for the metro in its middle.

Automation not only allowed Paris to remain as a model for technological innovations in the railway industry but also increases the number of lines in normal service when RATP workers are striking (MP 05 rolling stock).

In 2009, work commenced on installing platform screen doors; with Bérault and Porte Maillot being the first stations to be equipped.

During this time, individual stations were intermittently closed to allow platforms to be leveled with the height of the train floors (from fr:Ligne 1 du métro de Paris).

Franklin D. Roosevelt received a complete overhaul from its post World War II facade to a more contemporary & modern look.

This breakdown, described as historic by the RATP, is the consequence of a bug that occurred in the automatic pilot system which has been fitted in line 1 since 2013.