Pont au Change

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Construction of the section of the Paris Metro line 4, which runs alongside the Pont au Change under the Seine. In a complex and complicated process, several tubes of about 40 meters were laid under the Seine between 1905 and 1907. Using a wooden structure with lifting arms (to be seen in the picture), the tubes were lowered into the depths and then dug into the riverbed. Today, Line 4, with approximately 740,000 daily passengers (2013), is the most frequented of the entire Paris Métro network.