In the aftermath of the Spanish Civil War, the Francoist regime launched the so-called “Plan for the Fortification of the Southern Border” with the aim of attacking the British naval base on Gibraltar and controlling maritime traffic. The decision was made in the context of Spain’s alliance with Hitler and Mussolini during World War II, involving the forced labour of 30,000 young Republican prisoners. Under conditions of slavery, they undertook the gruelling task of installing long-range batteries, building bunkers, roads, pathways, and machine gun nests. This moving and insightful documentary gathers the voices of survivors from the “Disciplinary Workers' Battalions”, testimonies from local residents, and analysis from historians, together with archival documents, film, and photographs of the constructions, now known as the Muralla del Estrecho (Wall of the Strait). All with the hope—both for historical and democratic justice—that one day the name will be changed to the Muralla de los Prisioneros (Wall of the Prisoners).