The uprising and proclamation of the Catalan State on 6 October 1934, led by President Lluís Companys, returned the spotlight to the Castle. The military leaders who supported the rebellion were imprisoned in the Castle and it was the scene once again of court-martials and executions.
On 23 August 1936, the Committee of Antifascist Militias took possession of the Castle. With the aim of making this change of occupancy visible, a symbolic act was organised in which the parade ground became the Plaça de la Llibertat (the Liberty Square), a sign was hung at the entrance with the motto “Order, serenity and discipline”, and the Catalan flag was raised in a ceremony led by President Lluís Companys.
It soon went on to become a war base. The ERC militias were recruited there and it played an ineffective role as an antiaircraft gun position. Yet again, it was used for the internment and trial of political and military prisoners, with executions in the Santa Elena Moat. The main function of the Castle during the Civil War involved the repression and execution of the military leaders of the Alzamiento, sentenced by councils of war. Those accused of military rebellion were tried by military courts, and those accused of having Falangist or traditionalist affiliations and so on, by people’s courts. Following the events of May 1937, the prisoners held there were mainly accused of crimes of treason, espionage, sabotage, defeatism and anti-fascist dissent.
During the Civil War (1936-1939), nearly 1,500 people were imprisoned in Montjuïc Castle and about 250 were executed, mostly soldiers and civilians accused of high treason and espionage against the Republic. Only on 11 August 1938, sixty-two executions took place in the Santa Elena Moat.