Metro line 4: a line and its history

On 21 April 1908, metro line 4 opened to the public between Porte de Clignancourt and Châtelet stations. Here is its story. 

When metro line 4, the first north-south line, opened in 1908, it existed in two separate branches on the opposite banks of the Seine. It was the first time in history that a public transport line had to successfully cross the river. The ambitious plan paved the way for spectacular projects that took place at the heart of the French capital between 1905 and 1907. 

Given its trajectory, the line could only join Les Halles to rue de Rennes by crossing both arms of the Seine, and by passing through Île de la Cité, once upstream and once downstream. To accomplish this feat, two stations had to be built: Cité and Saint-Michel.

A bid to take the metro under the river

As the under-river crossing was by far the most complex phase in the construction of the line, a bid was launched to examine all possible solutions, and to designate the best project owner. The project proposed by Chagnaud was selected because it presented several advantages: it planned to sink caissons vertically into the riverbed, and instead of using twin tunnels, it would dig a single tunnel containing both tracks.

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Freezing the ground to let the metro through

The last and southernmost section of the Seine, over a 14.5-m stretch, used an original and revolutionary method for its time, which consisted of freezing the soil. An existing railway line (what is now RER line C) made it impossible to replicate the caisson technique that was used on the northern portions. The poor-quality soil was then frozen to allow leveling works to be conducted under the best possible conditions, by using brine-filled tubes that were frozen to -24°C. This technique hardened the ground in 40 days. 

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It was in January 1910 that metro line 4’s central section opened to the public between Châtelet and Raspail stations, thereby connecting both ends of the line: the northern section inaugurated on 21 April 1908, and the southern section inaugurated in 1909.

A line that continues to grow

But metro line 4 didn't stop there. It continued to operate in Paris proper between Porte d’Orléans and Porte de Clignancourt until 2013, when it was extended to Montrouge, before stretching farther afield to Bagneux in 2022. Since then, the line has been serving 29 stations over 14 kilometres.

The line is currently undergoing works to make it fully automated, running only automated trains across the line, by the end of 2023. Click here for more information.

Did you know ?

Metro line 4 is the only line in the network that allows connections with all other lines!

Metro line 4 art

Several artworks can be found along the distance of metro line 4.

One of them is the cultural installation titled Le Mythe Saint-Germain : un lexique amoureux (The Saint-Germain Myth: language of love) that was unveiled at Saint-Germain-des-Prés station in September 2021. The fresco showcases the neighbourhood’s cultural history and some its illustrious former residents, such as literary greats Boris Vian, Jacques Prévert and Simone de Beauvoir.

New artworks have been beautifying the length of the metro line 4 extension at Bagneux since January 2022. Let’s start with Ricardo Mosner’s imposing 105-metre-long mural that wraps around the new train repair centre in Bagneux. The work, which can be seen outdoors, illustrates several concepts, including the history of the city’s quarries, which provided the stones that were used to build Paris’ most beautiful monuments. Also featured: white-metal portraits of French Resistance heroine Lucie Aubrac, which were painted at the namesake station by street artist C215.

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