In the spring of 1942, Gen. Francisco Aguilar González, the Mexican ambassador to the Vichy government, left France to return to Mexico with his wife, Maria. The couple traveled through newly Fascist Spain to Lisbon, where she boarded a steamer bound for New York, with twenty trunks of their belongings, while the general made his way back across Spain, through France and then to London, eventually flying to New York for their rendezvous. In New York they boarded a passenger train with their belongings and traveled across the United States and Mexico before finally arriving at their home in Mexico City. Tucked away in one of the trunks and kept hidden for nearly seventy years were three small cardboard boxes given to Aguilar for safekeeping. They contained an archive of 4,500 negatives of photographs of the Spanish Civil War taken by three extraordinary photojournalists: Robert Capa, Gerda Taro and David Seymour (known as Chim).

Though Capa’s negatives had been missing for decades, rumors that a cache of them had been secreted away persisted. In 1979 Capa’s brother, Cornell, the founder of the International Center of Photography (ICP), in New York City, began a search for the lost images. He published an appeal in a well-known photography journal, and over time he managed to recover a number of lost works by Capa, Chim and Taro—but not the fabled negatives. They remained in Mexico, passing from Aguilar to his daughter, who gave them to her cousin, a filmmaker named Benjamin Tarver. In 1995, at an exhibition of Spanish Civil War photography in Mexico City, Tarver told the curator, a Queens College professor named Jerald Green, that he possessed images of similar scenes, which he believed were taken by Capa. Green relayed the information to curators at the ICP, but letters to the mysterious Tarver went unanswered, and the tantalizing lead vanished. In 2007, on behalf of the ICP, Trisha Ziff, a Mexico City–based documentary filmmaker, established contact with Tarver, and he agreed to meet her at a coffee shop. At a subsequent meeting he showed her three contact sheets with stunning images of Republican soldiers in battle and a woman dressed in black walking alongside a tank on a snowy battlefield. Ziff soon realized that these were the long lost negatives that Cornell Capa, who would die less than a year later, had been trying to locate. What had come to be called the Mexican Suitcase had finally been found.

The negatives in the Suitcase span the duration of the war, beginning with Chim’s foreboding photographs of marching Republican dignitaries in April 1936, three months before the conflict broke out, and ending with Capa’s stark portraits of Republican refugees in concentration camps in Southern France in March 1939. The distribution of the negatives among the photographers divides the war roughly into thirds, with Chim’s coverage heaviest at the beginning, Taro’s in the middle and Capa’s toward the end. A small number of the negatives correspond to previously published works—the Suitcase contains a famous 1936 photograph by Chim of a woman breastfeeding a baby at a rally for land reform—but the vast majority have never been seen by the public. A selection of the negatives is on display at the ICP through May 8. All 4,500 images, including a few touching shots of Capa and Taro in a Parisian cafe by a fourth photographer, the German-Jewish exile Fred Stein, are reproduced in an exemplary two-volume exhibition catalog published by the museum.

In an introductory essay to the catalog, the ICP’s chief curator, Brian Wallis, writes, “With their dramatic coverage of the Spanish Civil War, Robert Capa, Gerda Taro, and Chim invented modern war photography.” Remarkable as that achievement is, the newly discovered negatives do more than deepen our understanding of the origins of photojournalism or flesh out the biographies of three photographers, all of whom were killed on assignment. (Taro was crushed by a tank in Spain in 1937, Capa stepped on a land mine in Indochina in 1954 and Chim was shot by an Egyptian sniper days after the end of the Suez War in 1956.) The images convey the war’s complexities and offer a visual counternarrative to the revisionist view that the Republic was a monolithic Soviet satellite. Some photographs feature female soldiers and pro-Republican clergy. Others depict fleeing refugees, Communist generals, volunteers from the International Brigades, portraits of Federico García Lorca and La Pasionaria, and Republican guards protecting artistic treasures that belonged to the Francoist duke of Alba. Taken together, the images in the Mexican Suitcase portray a besieged country’s fight for its survival and its soul amid a Nazi-backed Fascist revolt. “The culture of the Spanish Republic,” Ziff said recently from her home in Mexico City, “was preserved in the Suitcase.”

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Chim, a Polish Jew whose given name was Dawid Szymin, was the most established of the three photographers. In 1932 he relocated to Paris from Leipzig, where he had been studying graphic arts, to pursue a degree in chemistry and physics at the Sorbonne. Amid rising anti-Semitism in Poland his father’s Yiddish publishing business struggled, and Chim was forced to work in order to continue his studies. He picked up a camera and began shooting street photography, focusing on portraits of the working class and unemployed of Paris. Within a year he was selling photos to Regards, which billed itself as “the illustrated newspaper of the Popular Front,” and later to Ce Soir, a Communist evening paper edited by the poet Louis Aragon. By all accounts Chim was a gentle, quiet man. Henri Cartier-Bresson, who later founded the Magnum photo agency with Chim and Capa, described him as “a philosopher, a chess player.” Perhaps it was this equipoise that enabled Chim to photograph unexpected moments of tranquillity amid chaos. A 1937 series of two boys playing in the ruins of Gijón after its destruction by Fascist bombers and naval artillery is one of the many revelations of the lost negatives.

Before the discovery of the Mexican Suitcase, Chim’s work in Spain was little known. He began covering the Republic in the spring of 1936, when Regards sent him to photograph the aftermath of the electoral victory by the center-left Popular Front coalition. Even then, with little experience as a photographer, Chim quickly mastered the captioned photographic essay, a narrative format favored by immensely popular new photo journals like Regards, Life and the British Picture Post. These essays typically featured some half-dozen photographs in an artful layout and told a story mainly with images. Often, Chim appeared to shoot with this format in mind: narrative sequences are found throughout his rolls. Besides their formal achievement, several of Chim’s essays open a pictorial window onto still-contentious aspects of the war.

In October 1936 Chim shot four rolls of film of Moroccan prisoners held by Republicans in a Madrid barracks. The pictures (none of which were published) show the prisoners eating, smoking cigarettes offered by Republican guards and smiling and laughing with their captors. Though the images showcase the Republic’s humane treatment of its captives, Chim’s extremely sympathetic portrayal of the Moroccans, especially a series of tender close-ups of three men in the final roll, is still surprising, given the reputation they earned for brutality. To augment the nearly 100,000 professional soldiers sent by Hitler and Mussolini to aid his revolt, Franco relied heavily on the Moroccans. They were his shock troops, dying at a rate of 1,000 a month in the long siege of Madrid. As the military historian Antony Beevor noted, they were also called on to inflict terror on the population. In Seville, in July 1936, Antonio Bahamonde, the press officer for the Fascist Gen. Queipo de Llano, an architect of the revolt, described watching the Moroccans throwing grenades into the windows of small houses in working-class neighborhoods, indiscriminately killing women and children. “The Moors took the opportunity to loot and rape at will,” he added. “Queipo de Llano, in his night-time talks…urged on his troops to rape women.”

Though the Moroccans, or Regulares Indigenas, held no particular allegiance to Fascism, they were desperately poor and easily recruited; the promise of a regular salary and food was especially enticing because the conflict in Spain followed a severe famine and drought in Morocco. “They took us as if we were cows. We knew nothing,” one veteran recalled in The Moroccan Labyrinth, a recent Spanish documentary about the Regulares. Another characterized his enlistment this way: “When you are hungry, you can’t see.” The Fascists further induced them by presenting their cause in religious terms, as a jihad against a godless enemy.

While most of the clergy in Catholic Spain also cast the war in religious terms, and overwhelmingly sided with the Fascists (the Primate of Spain, Cardinal Isidro Gomá, claimed the Republic was “controlled by the Semite International”), the Basque clerics, who shared their compatriots’ desire for greater autonomy, were a notable exception. In January 1937, in the Amorebieta Cloister, southeast of Bilbao, Chim shot a remarkable series showing Basque monks opening their refuge to Republican soldiers. The series includes several images of daily life inside the cloister: a monk conferring pleasantly with four Republican militiamen in the courtyard, soldiers setting up a radio transmitter and practicing formations and, most beautiful, a solitary monk studying a book in a small room with sunlight flooding through the window.

Chim’s work photographing the Basque clergy’s peaceful existence within the Republic was meant to counter the widespread belief that the government was inherently anticlerical. In the early months of the war, irregular militias killed several thousand clergy in the Republican zone (though few of these killings occurred in the Basque region). The Republican executions were a brutal and indiscriminate response to the church’s centuries-long alliance with the monarchy, its close fraternity with the estate owners in Spain’s semifeudal agricultural system and its fierce opposition to constitutional efforts to limit its power and role in civil society. These extrajudicial killings, however, contravened the government’s policy and were publicly condemned by the Socialist leader Indalecio Prieto. Republican President Manuel Azaña and Prime Minister José Giral reorganized the judicial system, establishing popular tribunals in an effort to stop the killings. By October 1936, they had subsided.

The church hierarchy’s unequivocal support for the Fascist rebellion was articulated in a pastoral letter written by the Bishop of Salamanca and published in September 1936. The letter described Franco’s adversaries as “sons of Cain” and the civil war as a “crusade in defense of religion, the Fatherland, and Christian civilization.” A year later, in response to the Nazi bombing of Guernica, which killed and wounded thousands of civilians and shocked many Catholics, Cardinal Gomá released an open letter to bishops around the world intended to shore up any wavering of Catholic support for Franco. The letter, signed by two cardinals, six archbishops and thirty-five bishops, characterized the Fascist revolt as the only recourse for “maintaining order and peace.”

Soon after Chim photographed the Amorebieta Cloister, he traveled to a remote mountainous area near the Basque village of Lekeitio and shot an even more confounding scene: a Basque priest saying an elaborate Mass to several dozen Republican soldiers before they went off to fight. Chim photographed the scene from four different angles, but the most arresting image, published prominently in Regards, is photographed from above. The camera looks down on a priest behind a makeshift altar leading Republican Catholic soldiers though the sacrament with a pastoral setting as his backdrop.

Despite mitigating factors like Azaña and Giral’s efforts and the loyalty of the Basque Catholics to the Republic, let alone the question of whether the destruction of cities like Guernica by aerial bombardment was justifiable to “maintain peace” in Catholic theology, the Vatican staunchly supported the Fascist insurgency. In August 1937 Rome accepted Franco’s diplomatic emissary, granting the insurgency de facto recognition. Following the Republic’s defeat, Pope Pius XII, who was later accused of remaining silent while millions of European Jews were deported to Auschwitz and other extermination camps, gave a radio address describing his “immense joy” with the Fascist triumph.

While the Pope’s radio address emphasized the Republican killing of Catholic clergy, he failed to note a different crime against the church. In October 1936 Fascist forces executed by firing squad sixteen Basque priests. The Pope’s address also made no mention of the 500 Basque clergy driven into exile by Franco and his accomplices. For them, the loyalty of the Basque Catholics was an international embarrassment that needed to be punished severely. Neither the Vatican nor the Spanish clerical establishment publicly condemned the murder of the Basque priests.

Remarkably, that silence continues today. Three years ago, Pope Benedict beatified 498 priests, nuns and other religious Catholics killed during the civil war, but none of the Basque priests were among them. As El País and the Association for the Recovery of Historical Memory, a Spanish human rights group, have documented, the list included clergy who were openly supportive of the Fascist uprising and in some cases aided it.

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The photos by Gerda Taro in the Suitcase reveal a passionate, fearless photographer whose wide-ranging coverage—trench warfare, peasants harvesting wheat, an international writers conference in Valencia—gives a sweeping picture of life inside the Republic. Taro, whose given name was Gerta Pohorylle, and was the daughter of Polish Jews, fled her native Germany in 1933, after being arrested during a Nazi raid. She moved to Paris, a refuge for many Eastern European émigrés; she met Capa in the fall of the following year, and the two fell in love. During a summer holiday in the South of France, with Capa’s encouragement and tutelage, she began shooting photographs. When the pair returned to Paris they shared an apartment and formed a loose-knit creative partnership. Taro, who also worked as an editor at a photo agency, acted as Capa’s manager, and the two developed various projects for collaboration.

Their most ambitious, and last, would be covering the civil war. Capa and Taro first traveled to Spain in August 1936, as freelancers without an assignment (Taro had yet to be published). Their appearance in the Suitcase begins picking up in February 1937, with a detailed look at the Republican defense of Madrid. Taro focused on the neighborhood around the university, and her attention to granular details—sandbag barricades, men positioning themselves in makeshift trenches—conveys both the anxiousness of the moment and the city’s bleak ambience. (She also captured a surreal image of a large brown bear sitting above a trench as two Republican soldiers talk obliviously.) At the beginning of her brief professional career her work was often uncredited. Later, she and Capa shared a credit, and three months before she died Taro began using only her name for some assignments. Mainly for this reason it has been difficult to determine the authorship of some of her works, but by piecing together her travel itinerary, among other clues, Taro scholars and ICP curators have done a painstaking job of establishing her contribution.

Shortly after photographing the university district, Capa and Taro photographed a nearby area newly decimated by German and Italian bombers. Taro’s images of what had been a densely populated neighborhood include a young woman collecting firewood among the rubble and two horses grazing in a street of ruins. Mainly her photos show the effects of the bombings on the faltering buildings. Three months later, in Valencia, Taro photographed the human casualties of Fascist air raids. She begins with a small crowd of desperate faces pressed up against the metal gate of the city morgue. She then moves inside the morgue and, in images that evoke Goya, lays bare the human face of saturation bombing: a middle-aged man, his head and face bleeding, lies unattended on a marble slab; a child lies on the floor, her summer dress splattered with blood; and most haunting, a man lies on the floor, partly covered in a blood-soaked white sheet, with a yearning expression frozen on his face.

The war’s fateful role as a precursor to World War II is vividly captured in Taro’s account of the Valencia morgue. It was confirmed during the Nuremberg trials when Hermann Göring, the Reich commissioner for aviation, testified that he urged Hitler to give Franco military support partly “to test my young Luftwaffe at this opportunity in this or that technical respect.” Göring’s “technical” experiments would take the form of the first use of carpet-bombing on civilian populations. The Fascists targeted dense cities like Madrid, Barcelona and Valencia in order to inflict the maximum amount of terror and civilian casualties. That the Nazis were simply preparing themselves for the next war was something lost on few. The headline in Regards over Taro’s Valencia pictures read “Dress Rehearsal for Total War.”

Two months later, covering the Battle of Brunete, outside Madrid, Taro was run over by an out-of-control Republican tank in a chaotic retreat. She died hours later. Her spare, elegant tombstone, designed by Alberto Giacometti, read “Gerda Taro, 1911 [sic]–1937, photojournalist for Ce Soir, killed July 25, 1937 on the Brunete front, Spain, in the line of duty.” In 1942, during the Nazi occupation, the inscription was replaced with a concrete block noting only her name and date of birth and death. She was the first female photojournalist to die on assignment.

In the exhibition catalog, Brian Wallis describes the controversy over Robert Capa’s most iconic photograph of the Spanish Civil War, Falling Soldier, as the primary motive behind the search for the lost negatives. The picture shows a solitary Republican soldier at the moment of getting shot and falling to his death on a hillside. Since the 1970s a fierce debate has raged as to whether the picture was staged. “It was in an effort to answer such charges—or at least understand that photograph more fully—that Capa scholar Richard Whelan and I set out in 2006 to try to find the picture’s missing negative,” Wallis writes. The curators did not find the lost negative to Falling Soldier in the Suitcase, but breathtaking images of Catalan orphans, the battles of Teruel and Ebro and especially of the Spanish exiles in concentration camps in France suggest that the emphasis placed by Capa’s defenders and accusers alike on a single image’s provenance has overshadowed the groundbreaking and courageous aspects of his work.

Capa left Spain in July 1937, shortly before Taro’s death. Heartbroken by the loss, he returned in late December, covering the battle of Teruel, a last-ditch Republican counteroffensive that briefly recaptured this provincial capital from Franco. The many rolls of film devoted to the battle show Ernest Hemingway smoking with Republican officers, a group of soldiers on a stairwell of a bombed-out building and two old women, one with a cane, dressed in black and walking arm in arm along a mountain pass. There is a photo of a dead Republican watchman in a tree, apparently electrocuted and caught among wires and branches fifteen feet in the air. Capa took the picture from a low angle, a favorite position of his, against an open expanse of sky. His compassion is most palpable in his widely published portrait of a man with an extinguished cigarette in his mouth, carrying his son, whose leg is wrapped in a bloodstained white cloth, to safety.

Among the images in the Teruel rolls are many pictures of Republican refugees, who app  ear frequently in all three photographers’ work, from the beginning of the war until the end. All three seemed to have a special feeling for them, but Capa’s pictures of the refugees are more frequent and profound. When he was 17, Capa was briefly arrested and beaten by the Hungarian secret police for his leftist activities. Two months later he fled Hungary and settled for a short time in Berlin. While there, he took to photography as a way to try to make a living. After the Reichstag fire he fled again, eventually settling in Paris. Like Chim and Taro, Capa changed his name (he was born Endre Friedmann) partly to conceal his émigré past.

In the beginning of 1939, with the Republic’s defeat inevitable, thousands of Republican exiles, fearing Franco’s retribution, began fleeing the country. Most of them traveled to France, where they were interned in concentration camps near the Spanish border. Remedios Oliva Berenguer, now 92, was 20 when she left her home outside Barcelona with her family. “We left at 11 pm and got to Figueres at 6 pm,” she said recently from her home in France.

There were bombers overhead and the road was full, full, full with people, with cars, with animals. We didn’t want to leave because the bomber planes were overhead. There was also a castle in Figueres, and it was being bombed nonstop…. We didn’t want to go to France. We wanted to go to the countryside, to stay with farmers in the Spanish countryside…. Trucks came for the women and children, but the trucks would arrive already full. People were so afraid they would jump on the trucks anyway and just hang from the sides. We crossed into France on February 7. It was about 6 pm that day. We all slept in the truck. We woke up the following day. We were about twenty-five kilometers from the border. It was sunny. The road was filled with people, filled with police, and they stopped us. We couldn’t go through. There was nothing there for us at the Argelès camp. No bathrooms, nothing. They did not expect us. Nothing was prepared, no planning. We then saw a truck arrive with bread. People just flocked to it. There was no organization. So they just tossed the bread out like we were dogs. They threw it on the ground and we picked it up. Then other trucks came with rolls of barbed wire, and we didn’t know why. We were thousands standing about, thousands. In the beginning, at the Argelès camp, there were about 75,000 of us. It was just the sand and sea. We were at the edge of the sea. So they constructed a barbed-wire fence along the side of the road to pen us in. The fences were at least two meters high. We knew we were among the first to arrive, but by the end we knew we numbered at least half a million people.

In March 1939 Capa journeyed to Argelès-sur-Mer, the camp where Oliva Berenguer and her family were interned, to document the fate of the exiles. His negatives show refugees living in threadbare tents under the open sky and men crouched on the ground eating meager rations. At the nearby camp at Le Barcarès, Capa photographed several men trapped behind a barbed-wire fence speaking to a passer-by on the other side. Later, he shifts his attention to a dozen men lying on the ground, huddled together for warmth near the camp’s outer fence.

Shortly before the outbreak of World War II the male prisoners were allowed to leave the camps to join the Foreign Legion or enlist in work brigades. Still others escaped. During the war, thousands of Republican exiles continued their fight, with the French Resistance and the Free French Forces. In all, an estimated 15,000 Spanish exiles died at the camps in France and 10,000 more died after they were deported from France to Mauthausen and other Nazi camps. As the civil war scholar Paul Preston notes, Franco encouraged Hitler to deport the Republican refugees to the German camps.

A significant percentage of the refugees emigrated to Mexico, the only country besides the Soviet Union to aid the Republic. During the war the Mexican government, though poor, sent arms to Spain as well as food and other humanitarian aid. “It’s not for no reason that the Suitcase was in Mexico,” Ziff told me. After Franco’s victory, Mexican President Lázaro Cárdenas agreed to accept an unlimited number of refugees provided their transport and accommodation were paid for. Republican relief organizations worked together with Mexican officials to bring them. Some 25,000 Spanish exiles eventually resettled in Mexico, their presence, like the negatives, preserving a fragment of the Spanish Republic.

After describing her journey, Oliva Berenguer recalled some of those who weren’t fortunate enough to make it to Mexico or survive the French camps. “There were mass graves filled with people who disappeared from the countryside,” she told me. “We had a neighbor who stayed behind in Spain. We later learned what happened to this man. He was about 58 years old and was a poet and a worker. He had a poet’s soul. Of course he was a Republican. His sons had left to fight. I think he lost two or three sons. And he was executed in the Montjuïc castle in Barcelona. He was killed simply because he was a Republican. He was against Franco and wrote poetry favoring the Republicans. He was just a man, who was 58 years old, and was executed.”