Paris built a 427-kilometre underground postal network powered by compressed air, delivering millions of letters and telegrams across the city in about two hours before maintenance problems led to its closure in 1984

Paris once operated the world's largest pneumatic postal network, stretching 427 kilometres beneath the city's streets by 1933. Using compressed air, the underground system transported messages and letters in special containers between post offices, delivering correspondence in approximately two hours. Originally developed to speed up telegram transmission, the network opened to public correspondence in 1879 and became an important part of Parisian communications. However, ageing infrastructure, rising maintenance difficulties and the growing use of telephones, telex and fax gradually reduced its importance. After more than a century of operation, the pneumatic postal service was discontinued on March 30, 1984.How did Paris's pneumatic postal network use compressed airAccording to the Committee for the History of the Post Office (CHP), the pneumatic postal network used compressed air to move containers carrying messages through underground tubes. These containers, known as cursors, travelled between connected postal and telegraph offices. The Paris system initially relied on water-powered equipment to produce compressed air, rather than the vacuum-based method used in London. According to the CHP's historical account, the administration later introduced steam-powered machinery in 1871 and gradually extended its use across the network from 1879. The system was subsequently improved through changes to its machinery, tubes and terminals to accommodate increasing numbers of dispatches.A major development came on January 25, 1879, when the administration established a public pneumatic postal service. Until then, the network had primarily supported the transmission of telegrams. Following this decision, members of the public could send open or closed forms through the service, while express letters were introduced in 1898. The network was extended across the Paris districts, and additional staff were employed to manage the growing volume of correspondence. According to the CHP publication, delivery to recipients generally took approximately two hours, making the service particularly useful for businesses, government offices and people who needed messages delivered quickly.How large was Paris's pneumatic postal network by 1933By 1933, the Paris pneumatic postal network had reached 427 kilometres of underground tubes, making it the largest network of its kind in the world. It connected postal offices across the capital and supported the movement of messages through a system of interconnected routes. The network was not limited to a small number of central offices; it had become an established part of the city's communications infrastructure. According to the CHP publication, the service was profitable at the time and employed specialised staff responsible for loading, transmitting and distributing dispatches, as well as maintaining the machinery.The network continued to serve Paris during the 20th century and experienced a significant increase in use during the Second World War. The CHP publication records that the volume of items transported increased from four million in 1940 to 16 million in 1945. However, the system gradually faced technical and financial difficulties. Although improvements were introduced, including the electrification of machinery and experiments with automated operations, these changes were not implemented across the entire network. Plastic tubes, which offered advantages over the earlier steel versions, also began replacing them only from 1965 and through occasional interventions.Why did Paris's pneumatic postal network begin to declineThe decline of the pneumatic postal network became increasingly apparent during the 1970s and early 1980s. According to the CHP publication, blockages involving the moving containers became more frequent, while maintenance problems left large sections of the network unusable. By 1983, slightly more than half of the lines could no longer operate. In areas where the underground system was unavailable, correspondence had to be transported above ground using cyclists or motorcyclists. The cost of maintaining and renewing the extensive infrastructure also became increasingly difficult to justify as the volume of mail carried by the network declined.The growing availability of alternative communication technologies further contributed to the decline. Telephone communications expanded, while telex and fax services became increasingly accessible to businesses that had previously relied on pneumatic deliveries. The volume of pneumatic dispatches fell from four million at the beginning of the 1960s to 2.7 million in 1973 and 650,000 in 1982. The service was eventually discontinued on March 30, 1984, at 5 pm, bringing an end to the Paris-wide pneumatic postal network. Some independent pneumatic systems continued operating at locations such as La Salpêtrière Hospital, the Paris-Favorites postal cheque centre and the National Assembly.You use AI every day. Now get your AI Quotient. Take the AIQ test.