Despite its reputation—per Walter Benjamin—as the “capital of the 19th century,” Paris came a little late to underground mass transit: after London (1863), Budapest and Glasgow (1896), Boston (1897), and Vienna (1898), the City of Light opened its first stretch of subway on July 19, 1900, halfway through that year’s Exposition Universelle. Initially six miles long, Line No. 1 linked Paris’s eastern and western extremities. Today, as this new exhibition recounts, it is part of the French capital’s 124-mile-long underground and elevated Métropolitain network, which, if all goes according to plan, will be extended to a mammoth 250 miles between now and the 2030s.