Canalul Dunăre-Marea Neagră
In 1956, Coposu was sentenced to life imprisonment for "betrayal of the working class" and "crime against social reforms". In April 1964, he was freed after 15 years of detention and 2 years of forced residence in Rubla (Brăila County), having spent, in all, 17 years of incarceration in 17 notorious detention and hard labor facilities associated with the communist regime, including Sighet Prison, Gherla Prison, Jilava, Râmnicu Sărat Prison, Pitești Prison, and the Danube–Black Sea Canal (where he was imprisoned with his friend and collaborator Șerban Ghica).