It begins with a photograph. In 1934 a struggling Hungarian photographer, André Friedmann, living in exile in Paris, is commissioned to take publicity pictures for a Swiss life insurance company's advertising brochure. On the lookout for potential models, he approaches a young Swiss refugee, Ruth Cerf, in a café on the Left Bank and convinces her to pose for him in a Montparnasse park.  Because she does not entirely trust the scruffy young charmer, Ruth brings along her friend Gerta Pohorylle, a petite redhead with a winning smile and a confident manner. So begins the most iconic relationship in the history of photography, and an intertwined and complex story of radical politics, bohemianism and bravery that, in the intervening years, has taken on the shadings of a modern myth.  Together, André Friedmann and Gerta Pohorylle would change their names and their destiny, becoming Robert Capa and Gerda Taro, the most celebrated visual chroniclers of the Spanish civil war. Together, too, they would change the nature of war photography, reinventing the form in a way that resonates to this day. Capa went on to become the most famous of the two, and arguably the most famous war photographer of the 20th century due to his visceral images of the D-day landings on Omaha Beach in Normandy. His most famous quote would become a dictum by which ensuing generations of war photographers worked: "If your pictures aren't good enough, you're not close enough."  This brave, but cavalier, approach to getting pictures of the action from within the action would cost both Gerda Taro and Robert Capa their lives – the former killed on the frontline of the Spanish civil war in 1937; the latter blown up by a land mine in Indochina in 1954. The myth of Robert Capa and Gerda Taro continues apace today with the British publication of a novel called Waiting for Robert Capa by Susana Fortes, a Spanish novelist and teacher. The book won the coveted Premio Fernando Lara in Spain on its initial publication in 2009 and has since been translated into 20 languages; the film rights have been bought by Michael Mann, the award-winning director of Heat (1995), The Insider (1999) and Public Enemies (2009). Fortes's short novel is essentially a historical romance that concentrates on the relationship between Capa and Taro. While the historical settings are accurate, Fortes literally puts words into each of their mouths, imagining conversations, thoughts and debates as well as accentuating both the doomed romance and the reckless bohemianism of the times.  With the Spanish civil war as its main backdrop, the narrative is an uneasy, sometimes awkward, merging of fact and fiction, and will almost certainly offend the many guardians of both Capa and Taro's reputations just as it will no doubt entrance the mainstream cinema-going audience should it be made into a Hollywood film. "I tried to be very respectful of the facts – the biographical data, the locations etc," says Fortes when I contact her in Spain, where she is on a book publicity tour. "I went through everything I could find: letters, memories, biographies… But for a novel to breathe, you have to build souls for your characters. This is reflected in the dialogue, the literary tension, the humour, the fights, the passion, the sex, the mixed feelings. In other words, life. That's part of the novelist's job. One always writes with one foot on the ground and the other in the air. It is the only way to walk the path."  However, when I mention the book to Jimmy Fox – veteran photographic historian and erstwhile director of the famous Magnum agency, which Capa co-founded with Henri Cartier-Bresson – he says: "I was dismayed by the novel. It was so fluttery and sugary. I think it is wrong to elevate the romance in that way. Capa was a flamboyant guy, a great drinker and a womaniser who had so many lovers, including Ingrid Bergman. Taro found the love of her life in Ted Allan, the man who was with her when she was fatally wounded. But of course that does not fit the big simplified romantic version so neatly."  The independent filmmaker Trisha Ziff, who directed The Mexican Suitcase (2010) about the discovery of a hoard of unseen negatives by Capa, Taro and David "Chim" Seymour, concurs. "Waiting for Robert Capa is a fiction based on a romance, but it is also a romance based on a fiction. If it becomes a Hollywood film, the myth will no doubt take over."  If there is one thing all the experts agree on, it is that nothing was straightforward about Robert Capa and Gerda Taro's relationship. Shortly after their first meeting, the young André Friedmann was sent to Spain on an assignment for a Berlin-based photo magazine. He subsequently photographed the Holy Week procession in Seville and described the festivities to Gerta Pohorylle in a letter that also mentioned how much he was thinking about her. On his return, he spent the summer holidaying in the south of France with Gerta and her friends. According to Ruth Cerf, quoted in Alex Kershaw's book Blood and Champagne: The Life and Times of Robert Capa, the pair "fell in love in the south of France" despite her suspicion that he was "a rogue and a womaniser". If the young Gerta was fascinated by his waywardness, he in turn was taken by her independent spirit. "Here was a woman," writes Kershaw, "who didn't suffocate him with affection, and who was as unashamed by her sexuality as she was conscious of her outsider status in Paris as a German Jew." This gets to the heart of the couple's mutual attraction: their shared radicalism and acute sense of exile. Friedmann had departed his native Hungary for Berlin in 1931 soon after his arrest by the secret police for leftist student activism. In February 1933, aged 19, he had fled Berlin when Hitler assumed power, travelling to Vienna, then back home to Budapest, before departing Hungary for good in September to live in penury in Paris, where he met Pohorylle on that fateful day in 1934.  By then, she too had experienced radical politics, arrest and flight. Born to bourgeois parents in Stuttgart in 1910, Pohorylle joined a young communist organisation and, around the time Friedmann was fleeing Berlin, was distributing anti-Nazi leaflets and putting up communist propaganda posters on walls under cover of darkness. She was arrested by the Nazis on 19 March 1933 and interrogated about a supposed Bolshevik plot to overthrow Hitler.  On her release, she used a fake passport to travel overland to Paris, where she was looked after by a communist network. Both André Friedmann and Gerta Pohorylle, though still young, were already seasoned activists and exiles when they met, intent on forging new lives for themselves while also staying loyal to their radical leftist roots.  Though Friedmann could seldom afford to buy film and often had to pawn his camera to survive in Paris, he schooled Pohorylle in the rudiments of photography and found her a job in the newly formed Alliance Photo picture agency. And she, it seemed, anchored him – at least for a while. "Without Gerta, André would not have made it," the late Eva Besnyö, another Hungarian photographer who mixed in the same bohemian circles in Berlin, told Kershaw. "She picked him up, gave him direction. He had never wanted an ordinary life, and so when things didn't go well, he drank and gambled. He was in a bad way when they met, and maybe without her it would have been the end for him."  As Friedmann's photographic career tentatively took off in Paris, his younger brother Cornell joined him, developing the photographs taken by André as well as those of his friends, Henri Cartier-Bresson and David "Chim" Seymour, in a darkened bathroom in a hotel that overlooked the famous Café du Dôme. It was there that the three photographers mingled with philosophers, writers and artists, drinking and dreaming of better times. It was around this time also that André Friedmann and Gerta Pohorylle became Robert Capa and Gerda Taro in a shared act of self-reinvention that still seems daring today.  The first anyone else heard of Robert Capa was when the couple turned up at the offices of Alliance Photo and announced they had discovered a famous American photographer of that name. The pair soon found they could sell photographs attributed to the fictitious Capa to French photographic agencies for three times the price of Friedmann's, such was the status accorded visiting American photographers. Their joint ruse was soon discovered, but the pseudonyms remained in place. In her essay for the exhibition catalogue Gerda Taro: Archive, published in 2007, Irme Schaber notes: "Taro and Capa were not merely reacting to their precarious economic situation. They were responding as well to the antisemitism of Germany and the increasing antipathy towards foreigners in France. And to elude the stigma attached to being refugees, they spurned every ethnic or religious label."  If their joint self-reinvention was the first significant factor in the dramatic trajectory of Robert Capa and Gerda Taro, the second was their decision to go together to Spain in 1936 to cover the republican resistance to Franco's fascist rebels. Like many writers and artists, including George Orwell and André Malraux, they went there out of political conviction and scorned any notion of journalistic detachment. The fight against fascism was, in a very real and personal way, their fight, given their history as exiles and refugees, and the Spanish civil war was the literal and metaphorical frontline of that battle.  It was an adventure, though, that almost ended as soon as it had begun, when the plane hired by the French magazine Vu to take them to Barcelona crash-landed in a field on the outskirts of the city. The pair limped into Barcelona to find scenes of ferment and disorder as anarchist forces took over the city. There, they photographed young republicans leaving Barcelona for the frontlines. Then in September they travelled together to the front themselves, arriving in the village of Cerro Muriano near Córdoba, where they found, and photographed, crowds of villagers fleeing their homes as the fascists rained shells down on the village. In one famous series of pictures, Capa captured Taro crouched, camera in hand, behind a wall beside a republican soldier. In another even more famous picture, perhaps the most well-known war photograph ever, Capa caught a militiaman at the very moment of his death from a sniper's bullet.  In that split second, the legend of Robert Capa, war photographer, was born, and decades later that same image would become the centre of a debate that still simmers over the ethics and veracity of war photography. In Waiting for Robert Capa, Fortes writes: "Death of a Loyalist Militiaman contained all the drama of Goya's Third of May 1808 painting, all the rage that Guernica would later show… Its strength, like all symbols, didn't lie in just the image, but in what it was representing." Fortes also imagines Taro gently probing Capa for the story of what really happened that day, and him replying: "We were just fooling around, that's all. Perhaps I complained that everything was far too calm and that there wasn't anything interesting to photograph. Then some of the men started to run down the slope and I joined in as well. We went up and down the hill several times. We were all feeling good. Laughing. They shot in the air. I took several photographs…"  Though the context of the photograph is still contested, the imagined conversation does describe what probably happened that day just before a Francoist sniper returned fire from across the hills, killing the militiaman who was running down the hill for Capa's camera. "People want the truth from war photography more than they do from any other kind of photography," says Jimmy Fox, the Magnum picture editor who has worked with the likes of Don McCullin and Philip Jones Griffiths, "but a flat surface of an image is not the reality and never can be."  In Spain, Capa soon developed a reputation for taking photographs whatever the risk, setting the tone for war reportage as we now know it. Taro, too, was often seen running across the battle lines with her camera, her bravery matched by her recklessness. She travelled back and forth to the frontlines, shooting what she saw, often driven by a mixture of humanity, political commitment and a shrewd understanding of the power of the photograph to shape public opinion.  Throughout 1937, Taro visited several frontlines, either with Capa or on her own. They managed to return to Paris for a short vacation in July that year, celebrating Bastille Day by dancing in the streets below Sacre Coeur and, according to Schaber, hatching "great plans for the future". Taro then returned to Spain alone, despite the growing concerns of her friends who, having seen her recent photographs of the fighting, feared for her safety.  Defying a ban on journalists travelling to the front, she once again made her way to Brunete with the Canadian journalist Ted Allan, her close friend, travelling companion and soon-to-be lover. According to Allan's diaries, written later, they spent "mornings afternoons and evenings together chasing stories... For three or four weeks we were constant companions. And finally, one afternoon, we ended up in her hotel room." She told Allan: "Capa is my friend, my copain," and said she might be travelling to China with him. "Nothing was settled," wrote Allan. "Everything was possible."  On Sunday 25July, the pair found themselves trapped in a foxhole near Brunete as bombs fell around them relentlessly. Taro kept on photographing, often holding her camera high above her head to capture the carnage. Allan protected her with a film camera as shrapnel and rocks fell around them. Then, as republican troops began pulling out of the area, Taro and Allan ran out of the foxhole and hitched a ride on the running board of a car while the planes continued to strafe the retreating convoy. In the chaos, the car was then rammed by an out-of-control republican tank and the couple were thrown into the dirt. Transported to a nearby field hospital, Taro died from her injuries in the early hours of the following morning. She was 26. The injured Allan did not get to see her again. According to Irene Golden, the nurse who was on duty, her last words were: "Did they take care of my camera?"  Gerda Taro's funeral in Paris was attended by tens of thousands of mourners, including Capa, Chim and Ted Allan. Orchestrated by the French communist party, which claimed her as one of its own, it became, as Schaber puts it, "a spectacular manifestation of international solidarity with the Spanish republic". In death, Gerda Taro became a hero. Robert Capa went on to become the most celebrated and mythologised war photographer of the century until he, too, died in action in Indochina in 1954 at the age of 40. "He never talked about her," says the photographer Ata Kandó in The Mexican Suitcase.  Gerda Taro has now fully emerged from the shadow of Capa as an important photographer in her own right. Many photographs attributed to him – they initially shared the byline CAPA – have now been identified as hers. "She was a pioneering woman both as a photographer and a political activist," says Ziff. "She was very liberated for her time, putting her work before any more traditional female role. She had reinvented herself – but the Capa myth was so strong that, even when she died, some newspapers described her as Robert Capa's wife. Their lives were entwined, but she was very much her own woman, and he knew that. They both believed that their photographs could change the world and change the way people think. And their photographs did."  For details of The Mexican Suitcase, go to themexicansuitcase.com. Robert Capa: The Paris Years 1933-54 by Bernard Lebrun, featuring pictures by the photographer, is published by Abrams, £24.99; and Waiting for Robert Capa by Susana Fortes is published by HarperPress
Capa and Taro lived, loved and died on the frontline, becoming the most famous war photographers of their time. As a new novel about them is published, Sean O'Hagan explores the real nature of their relationship