It was market day in Guernica one afternoon in May 1937, when the church bells of Santa Maria sounded the alarm. People from the surrounding hillsides had crowded the town square. Seventy percent of the town was about to be destroyed - and sixteen hundred civilians - one third of the population - killed or wounded. For over three hours, around twenty-five of Germany's best-equipped bombers, accompanied by at least twenty more Messerschmitt and Fiat Fighters, dumped one hundred thousand pounds of high-explosive and incendiary bombs on the village, slowly and systematically pounding it to rubble. Those trying to escape were cut down by the machine guns of fighter planes. The fires that engulfed the city burned for three days. The bombardment of Guernica rapidly became a world-renowned symbol of the horrors of the Spanish Civil War - which marks its 70th anniversary on Tuesday (July 18.) 35,000 volunteers from more than 50 countries fought in defence of the left-wing Spanish Republican government, battling an insurgency by right-wing fascist General Francisco Franco. It was the first war where civilians were systematically targeted. News of the Guernica bombing spread like wildfire. The Nationalists immediately denied any involvement, as did the Germans. But few were fooled by Franco's protestations of innocence. Guernica resident Maria Ines was a baby when the town was bombed. She has heard the story many times from her mother. "She said that my grandmother came to this square that day with a donkey - and me in her arms. They were very concerned looking for her, because there had been a lot of people killed," she said. Zurine, a sixty four year old woman, lost her father in the attack. It is too painful for her to describe his death. All she can say is how difficult her childhood was. "I was only five years old but I know that it was very hard for my mother to survive without my father with five children and being only 36 years old. There were many families equally destroyed," she said. Guernica today shows minimal signs of the attack. Remarkably, several significant sights were untouched - the historic Casa de Juntas, with its rich archives of the Basque race, where the ancient Basque Parliament used to sit; the famous 600 year old oak of Guernica; and the noble parish church of Santa Maria. Many analysts say the attack had a great influence on the generations of Basques who grew up with a strong sentiment of independence that has marked their desired to separate from Spain. "Franco was a dictator that didn't do much for the Basque region. Actually he destroyed it," fifteen year old Inaki, a student, said. The bombardment inspired one of Pablo Picasso's most famous paintings, known simply as Guernica. The painting was a symbol for Basque nationalism during the Spanish transition to democracy. Today a copy hangs in the lobby of the United Nations Security Council. The Spanish civil war waged for three years, with Franco supported by Hitler and Mussolini, and the Soviets backing the beleaguered Republicans. It ended with the collapse of the Republic in 1939, ushering in an authoritarian right-wing dictatorship which lasted until Franco's death in 1975. The numbers of civilian casualties is still hotly debated, with numbers ranging from 300,000 to up to a million.