The bombardment of civilians from the air was a regular feature of the Spanish Civil War from 1936 to 1939. It is estimated some 15,000 Spaniards died as a result of air bombings during the Civil War, most civilians, and 11,000 were victims of bombing from the Francoist side that rebelled against the Republican government, supported by German and Italian aviation that joined the rebellion against the Republic. In Catalonia alone, some 1062 municipalities experienced aerial bombardments by the Francoist side of the civil war. In cities across Spain, municipal and regional authorities developed detailed plans for civilian defense in response to these air campaigns. In Barcelona, the municipality created the Junta Local de Defensa Passiva de Barcelona, to build bomb shelters, warn the public of bombings, and educate them on how to protect themselves against aerial bombardment. They mobilized civilians around the concept of ‘passive defense.’ This proactive response by civilians and local government to what they recognized as a war targeting them is an important and under-studied aspect of the Spanish Civil War.