Rebel troops shelter behind a wall near a mountain road on the Sierra de Guadarrama front, while they engage government troops during the advance on Madrid, Spain. (Photo by Keystone/Getty Images). Circa 1936

Nationalist soldiers enter the town of Irun during the Spanish Civil War. (Photo by Keystone/Getty Images). September 1936

Spanish soldiers giving the Fascist salute. (Photo by Keystone/Getty Images). Circa 1937

A Spanish Loyalist supporter holding her gun during the Spanish Civil War. (Photo by Keystone/Getty Images). Circa 1937

Spanish government militia troops pictured taking a few hours' rest, the day after their attack on Huesca, during the siege of Barcelona. (Photo by Keystone/Getty Images). Circa 1937

Reporters at the front line with Spanish Republican troops. Ernest Hemingway can be seen (in glasses) in the background. Also the man posing for the photo on the left, holding the puppy, is George Orwell. (Photo by London Express/Getty Images). Circa 1937

A man trying to clear away the wreckage of a building at Madrid after bombing by rebel forces. (Photo by Hulton Archive/Getty Images). 1936

News reporters mingle with members of the International Brigade, amongst them is Ernest Hemingway (with mustache & glasses), during the Spanish Civil War. (Photo by London Express/Getty Images). Circa 1937

The “Artists Ambulance” on display at Palace Yard, London, before being sent to the civil war in Spain. Women of the Artists International Association organised an exhibition and sale of pictures, contributed by famous artists, and raised enough money to pay for the ambulance and £500 worth of supplies after just one and a half days. (Photo by Reg Speller/Fox Photos/Getty Images). 15th January 1937

A crowd of FAI militia (Iberian Anarchist Federation) prepare to leave the barracks at Pedralbes near Barcelona for the Sargasso front during the Spanish Civil War. (Photo by Fox Photos/Getty Images). 28th August 1936

A soldier in the French Frontier Troops feeding one of the Spanish refugee babies who had crossed the border from Spain during the Spanish Civil War. (Photo by Keystone/Getty Images). 3rd April 1938

Moorish troops guarding an outpost near Navalcanero which General Franco's army captured, during the Spanish Civil War. (Photo by Horace Abrahams/Keystone/Getty Images). 30th October 1936

A British army sentry on duty beside Spanish gendarmes at No Man's Land between Gibraltar and Spain during the Spanish Civil War. (Photo by Norman Smith/Fox Photos/Getty Images). 20th July 1936

Government troops leave Barcelona during the Spanish Civil War by train. (Photo by Central Press/Getty Images). Circa 1936

Militia men and women standing on a home made tank in Barcelona. (Photo by Fox Photos/Getty Images). 28th August 1936

Government troops perched on a tractor in a Barcelona street during the Spanish Civil War. (Photo by Fox Photos/Getty Images). 28th August 1936

A woman from Madrid leaving for the front during the Spanish Civil War. (Photo by Keystone/Getty Images). 27th February 1937

A youth parade of Spanish schoolchildren makes its way along the road wearing the black shirts of the Fascists and carrying dummy rifles. Their home of Irun has been taken over by Rebel troops during the Spanish Civil War, and they have been converted to the Fascist cause. (Photo by Maeers/Fox Photos/Getty Images). 13th November 1936

Captain Coche, government Chief of Transport, drinks communion wine from a chalice taken from a church in Buitrago during the Spanish Civil War, 8th September 1936. Buitrago was a small town near the dams, reservoirs, and aqueducts in the Sierra Norte range which were essential for supplying Madrid with water and for which there was a lot of fighting. (Photo by Fox Photos/Hulton Archive/Getty Images)

Artillery men of Franco's army in north-western Spain during the Spanish Civil War, 30th September 1937. A crucifix has been fixed to their gun sheild. (Photo by Keystone/Hulton Archive/Getty Images)

Fleeing Loyalists huddle under a blanket on the road to Perpignan during the Spanish Civil War, circa 1936. (Photo by Three Lions/Hulton Archive/Getty Images)

General Juan Bautista Sanchez of the 5th Brigade of Navarre addresses his troops in the outskirts of Madrid during the Spanish Civil War, circa 1936. (Photo by Three Lions/Hulton Archive/Getty Images)

A Republican farmer defending a farm on the outskirts of Irun against Nationalist forces during the Spanish Civil War, 6th September 1936. A comrade lies dead by his side. (Photo by Keystone/Hulton Archive/Getty Images)

A truckload of Loyalist soldiers are transported to a prisoner-of-war camp during the Spanish Civil War, circa 1937. (Photo by Three Lions/Hulton Archive/Getty Images)