On March 31, 1937, nine months into the Spanish Civil War, General Emilio Mola, the main figure in charge of the northern campaign by the military rebels against the democratically elected government of Spain’s Second Republic, issued the following chilling proclamation:
I have decided to end the war rapidly in the north. The lives and property of those who surrender with their arms and who are not guilty of murder will be respected. But if the surrender is not immediate, I shall raze Bizkaia to its very foundations, beginning with the war industry. I have the means to do so.
That same day, heavy bombers from Fascist Italy’s Legionary Air Force (Aviazione Legionaria) bombed the Bizkaian towns of Durango and Elorrio in relays over a period of five days.
Casualty figures, the vast majority of them non-combatants, are disputed, with different figures of between 150 and 350 deaths quoted by different authors, although the official number quoted at yesterday’s commemorations was 336. Churches were also bombed in Durango as part of the operation, resulting in the death of one priest and several nuns. Some images of the town in the aftermath of the bombing can be seen here.
This was arguably the first instance in history of aerial bombing of a civilian population on European soil. And it clearly served as an operational model for the bombing of Gernika, later that same month, on April 26.
For more on the general context in which these events took place, see Modern Basque History by Cameron Watson, which you can download for free here. For more detailed studies of the impact of the civil war in the Basque Country, check out War, Justice, Exile, and Everyday Life, 1936-1946, edited by Sandra Ott and Gernika 1937: The Market Day Massacre by Xabier Irujo.