Benito Mussolini ordered the bombing without informing Francisco Franco, his nominal ally in the Spanish Civil War. The Italian dictator was a disciple of General Giulio Douhet, the theorist who argued that wars could be won from the air through strategic bombing of civilian populations, breaking their will to resist. Barcelona was the test case. Mussolini personally directed the Aviazione Legionaria to conduct what he called a "continuous bombing of Barcelona diluted in time," a phrase that sanitized mass murder into strategic jargon. The bombers, Savoia-Marchetti SM.79s and SM.81s, carried Spanish markings to provide a thin veneer of deniability. The first raid came at 10 p.m. on 16 March, delivered not by Italian planes but by German Heinkel He 51 fighters, followed by the Italian waves at three-hour intervals through the next day and a half.

The Spanish Republican Air Force did not send fighters to defend Barcelona until the morning of 17 March, leaving the city exposed through the first night and into the following day. The Italian bombers' declared targets were military warehouses, arms factories, rail lines carrying soldiers, and the port. What they hit was everything: cinemas, consulates, theaters, apartment blocks. The working-class districts bore the heaviest damage on the night of 18 March. Some historians have described the raids as the first aerial carpet bombing in history, a distinction that Guernica is sometimes given but that Barcelona's scale and systematic timing may more accurately claim. The people of Barcelona had no underground metro system deep enough for shelter. They huddled in basements and building lobbies, waiting for each three-hour interval to pass, knowing another wave was coming.

Western democracies condemned the attacks, and even Franco was displeased. He had not been consulted, and on 19 March he asked Mussolini to suspend the bombing, not out of humanitarian concern but from fear of "complications abroad." The international press covered the horror in detail; Time magazine ran the story under the headline "Barcelona Horrors." But condemnation produced no intervention. The democracies that protested the bombing continued their policy of non-intervention in the Spanish Civil War, leaving the Republic to fight with little outside support beyond Soviet aid and the International Brigades. Barcelona fell to Franco's forces in January 1939, less than a year after the bombing. The lesson Mussolini drew from Barcelona, that terror bombing worked, would be tested on a far larger scale when the Second World War began six months later.

The bombing lives on in Barcelona's cultural memory. Carlos Ruiz Zafon opens his novel The Labyrinth of Spirits with the March 1938 raids, using the destruction as a portal into the city's haunted modern history. The neighborhoods that were destroyed have been rebuilt, but plaques mark the sites where bombs fell. The larger legacy is strategic: Barcelona proved that air power could terrorize a civilian population but could not, by itself, break a city's resistance. The Republic held Barcelona for another ten months after the bombing. When the city finally fell, it was to a ground army, not to bombs. Douhet's theory, which Mussolini embraced so enthusiastically, was shown to be both morally catastrophic and militarily incomplete. The people of Barcelona endured forty-four hours of sustained aerial attack and kept fighting. That endurance deserves to be remembered alongside the horror.