In the agricultural plain of Seine-et-Marne, between the communes of Seine-Port, Cesson, and Boissise-la-Bertrand, metal pylons have stood for over a century, rising above the fields of wheat and beetroot. The Sainte-Assise site, built in 1920, was once the most powerful transmitter in the world. It was designed to free France from reliance on foreign undersea cables, enabling direct communication with its colonial territories. The site features eleven pylons, each 250 meters tall, and five masts of 180 meters. Despite its historical significance, there are no signs or explanations, leaving visitors puzzled by the towering metal structures that dominate the landscape. Sainte-Assise was once a notable site for international visits. The President of the Republic hosted foreign leaders such as the négus of Ethiopia, the kings of Siam and Romania. In November 1921, the first experimental French radio broadcast was made using a 1 kW long-wave transmitter, with singer Yvonne Brothier performing several pieces. A century later, it's hard to imagine that French radio, as we know it today, originated in the same field where the current pylons now stand. The Sainte-Assise domain extends beyond its antennas. Around the castle that gives the site its name, there is a property spanning several hundred hectares. In 1922, Charles-Louis de Beauvau-Craon sold the estate to the Cie Radio France, leading to the installation of the transmitting station and the current array of antennas. The castle was transformed from an aristocratic residence into the administrative center of a military-industrial complex. During World War II, the Sainte-Assise transmitter was occupied by the German Navy to communicate with submarines and remained unscathed by bombing. After the Liberation, the Posts Administration took over the site. A major change occurred in 1991 when a portion of the estate was sold to the French Navy, becoming a military zone. Since then, Sainte-Assise has been part of a separate, highly secure world focused on ultra-sensitive transmissions. The Marine Communications Center, established in 1998, handles communications with submarines. An entire unit of marine riflemen patrols the area, ensuring the security of very long-wave signals that can penetrate seawater, enabling Paris to maintain contact with its nuclear-powered submarines. This secrecy explains why the area remains closed to the public. In December 2000, three of the unused 180-meter pylons were dismantled, reducing the density of the site. Part of the land has since been repurposed: a section is now a military area under the French Navy, while another became the Sainte-Assise Regional Heathland Nature Reserve in 2009. On this protected land, heathland has reclaimed its natural space, where once radio waves crackled. A few hundred meters away, Globecast, a subsidiary of Orange, operates the Sainte-Assise teleport, a satellite broadcasting facility with large parabolic antennas. This site supports the transmission of television and radio signals via satellite. Thus, two distinct narratives unfold on the same plain: one of secret underwater communications and the other of everyday satellite broadcasts that reach French homes every day.