Draped in lush trees and surrounded by stately buildings, Buenos Aires’ Plaza de Mayo might look like a place to check out monuments or stop for a relaxing rest. But each Thursday, one of Argentina’s most famous public squares fills with women wearing white scarves and holding signs covered with names.

They are the Mothers and Grandmothers of the Plaza de Mayo, and they are there to bring attention to something that threw their lives into tragedy and chaos during the 1970s: the kidnapping of their children and grandchildren by Argentina’s brutal military dictatorship.

For decades, the women have been advocating for answers about what happened to their loved ones. It’s a question shared by the families of up to 30,000 people “disappeared” by the state during Argentina’s “Dirty War,” a period during which the country’s military dictatorship turned against its own people.

In 1976, the Argentine military overthrew the government of Isabel Perón, the widow of populist president Juan Perón. It was part of a larger series of political coups called Operation Condor, a campaign sponsored and supported by the United States.

The military dictatorship that resulted called itself the “Process of National Reorganization,” or “Proceso,” and dubbed its activities the Dirty War. But the war wasn’t with outside forces: It was with the Argentinian people. The war ushered in a period of state-sponsored period of torture and terrorism. The junta turned against Argentina’s citizens, whisking away political dissidents and people it suspected of being aligned with leftist, socialist or social justice causes and incarcerating, torturing and murdering them.

The Dirty War was fought on a number of fronts. The junta dubbed left-wing activists “terrorists” and kidnapped and killed an estimated 30,000 people. “Victims died during torture, were machine-gunned at the edge of enormous pits, or were thrown, drugged, from airplanes into the sea,” explains Marguerite Feitlowitz. “Those individuals came to be known as “the missing,” or desaparecidos.”

The government made no effort to identify or document the desaparecidos. By “disappearing” them and disposing of their bodies, the junta could in effect pretend they never existed. But the family members and friends of the disappeared knew they had existed. They knew about the “death flights” in which bodies were flung from airplanes into bodies of water. They heard rumors about detention centers where people were raped and tortured. And they searched desperately for traces of their loved ones.

Among the desaparecidos were children born to pregnant women who were kept alive long enough to give birth to their babies, then murdered. Five hundred of those children, and others seized from their parents during the Dirty War, are thought to have been given to other families.

“In a final erasure, the dictatorship’s operatives stripped the women’s babies of their identities — many were kept as spoils of war by people close to the regime,” writes Bridget Huber for California Sunday Magazine. “Others were abandoned at orphanages or sold on the black market.”

In 1977, a group of desperate mothers began to protest. Every week, they gathered in the Plaza de Mayo and marched, tempting the ire of the military junta. “Government officials at first tried to marginalize and trivialize them by calling them “las locas,” the madwomen, but they were baffled as to how to suppress this group for fear of a backlash among the population,” writes Lester Kurtz.

Soon, the government turned against the protesting women with the same brand of violence they had visited on their children. In December 1977, one of the group’s founders, Azucena Villaflor, was kidnapped and murdered. Twenty-eight years later, her relatives received confirmation that she had been killed and dumped in a mass grave. Several other of the group’s founders were also kidnapped and presumably killed.

But the women didn’t stop. They protested throughout the 1978 World Cup, which was hosted by Argentina, and took advantage of international coverage to make their cause known. They protested despite state threats and at least once incident in which a portion of the group was fired on by machine gun-toting policemen during a protest. And in 1981, they gathered for their first “March of Resistance,” a 24-hour-long protest that became an annual event. Their activism helped turn the public against the junta and bolster awareness of a policy that counted on silence and intimidation to victimize dissidents.

Some of the mothers of the disappeared were grandmothers who had seen their daughters whisked away and presumably killed and their grandchildren given away to other families. Even after the Dirty War ended in 1983, the Grandmothers of the Plaza Mayo have searched for answers and worked to identify children who grew up without any knowledge of their true parents.

They found a powerful ally in Mary-Claire King, an American geneticist who began working with them in 1984. King and her colleagues developed a way to use the grandmothers’ mitochondrial DNA, which is passed on through mothers, to help match them with their grandchildren. The technique has led to controversies, as when it was used on the reluctant adoptees of a powerful media magnate who were forced to give over their blood for testing. But it has also led to the creation of a national genetic database. To date, the organization has confirmed the identities of 128 stolen children, largely using the database and DNA identification techniques.

The Dirty War has been over since the military junta gave up power and agreed to democratic elections in 1983. Since then, nearly 900 former members of the junta have been tried and convicted of crimes, many involving human rights abuses. But the chilling legacy of Argentina’s Dirty War lingers on—and until the mystery of the country’s missing children is fully solved, the mothers and grandmothers of the desaparecidos will keep fighting for the truth.