When the Sisters of Our Lady of Charity decided to sell some land they owned in Dublin, Ireland, to pay their debts in 1992, the nuns followed the proper procedures. They petitioned officials for permission to move the bodies of women buried in the cemetery at their Donnybrook laundry, which between 1837 and 1992 served as a workhouse and home for “fallen women.”

But the cemetery at Donnybrook was no ordinary resting place: It was a mass grave. Inside were the bodies of scores of unknown women: the undocumented, uncared-about inmates of one of Ireland’s notorious Magdalene laundries. Their lives—and later their deaths—had been shrouded in secrecy.

For more than two centuries, women in Ireland were sent to institutions like Donnybrook as a punishment for having sex outside of marriage. Unwed mothers, flirtatious women and others deemed unfit for society were forced to labor under the strict supervision of nuns for months or years, sometimes even for life.

When the mass grave at Donnybrook was discovered, the 155 unmarked tombs touched off a scandal that exposed the extent and horrors of the Magdalene laundries. As women came forward to share their experiences of being held against their will in restrictive workhouses, the Irish public reacted with outrage.

When the Magdalene Movement first took hold in the mid-18th century, the campaign to put “fallen women” to work was supported by both the Catholic and Protestant churches, with women serving short terms inside the asylums with the goal of rehabilitation. Over the years, however, the Magdalene laundries—named for the Biblical figure Mary Magdalene—became primarily Catholic institutions, and the stints grew longer and longer. Women sent there were often charged with “redeeming themselves” through lace-making, needlework or doing laundry.

Though most residents had not been convicted of any crime, conditions inside were prison-like. “Redemption might sometimes involve a variety of coercive measures, including shaven heads, institutional uniforms, bread and water diets, restricted visiting, supervised correspondence, solitary confinement and even flogging,” writes historian Helen J. Self.

Ireland’s first such institution, the Magdalen Asylum for Penitent Females in Dublin, was founded by the Protestant Church of Ireland in 1765. At the time, there was a worry that prostitution in Irish cities was on the rise and that “wayward” women who had been seduced, had sex outside of marriage, or gotten pregnant out of wedlock were susceptible to becoming prostitutes. Soon, parents began to send their unmarried daughters to the institutions to hide their pregnancies.

Initially, a majority of women entered the institutions voluntarily and served out multi-year terms in which they learned a “respectable” profession. The idea was that they’d employ these skills to earn money after being released; their work supported the institution while they were there.

But over time, the institutions became more like prisons, with many different groups of women being routed through the system, sometimes by the Irish government. There were inmates imported from psychiatric institutions and jails, women with special needs, victims of rape and sexual assault, pregnant teenagers sent there by their parents, and girls deemed too flirtatious or tempting to men. Others were there for no obvious reason. Though the institutions were run by Catholic orders, they were supported by the Irish government, which funneled money toward the system in exchange for laundry services.

Nuns ruled the laundries with impunity, sometimes beating inmates and enforcing strict rules of silence. “You didn’t know when the next beating was going to come,” said survivor Mary Smith in an oral history.

Smith was incarcerated in the Sundays Well laundry in Cork after being raped; nuns told her it was “in case she got pregnant.” Once there, she was forced to cut her hair and take on a new name. She was not allowed to talk and was assigned backbreaking work in the laundry, where nuns regularly beat her for minor infractions and forced her to sleep in the cold. Due to the trauma she suffered, Smith doesn’t remember exactly how long she spent in Sundays Well. “To me it felt like my lifetime,” she said.

Smith wasn’t alone. Often, women’s names were stripped from them; they were referred to by numbers or as “child” or “penitent.” Some inmates—often orphans or victims of rape or abuse—stayed there for a lifetime; others escaped and were brought back to the institutions.

Another survivor, Marina Gambold, was placed in a laundry by her local priest. She recalls being forced to eat off the floor after breaking a cup and getting locked outside in the cold for a minor infraction. “I was working in the laundry from eight in the morning until about six in the evening,” she told the BBC in 2013. “I was starving with the hunger, I was given bread and dripping for my breakfast.”

Some pregnant women were transferred to homes for unwed mothers, where they bore and temporarily lived with their babies and worked in conditions similar to those of the laundries. Babies were usually taken from their mothers and handed over to other families. In one of the most notorious homes, the Bon Secours Mother and Baby Home in Tuam, scores of babies died. In 2014, remains of at least 796 babies were found in a septic tank in the home’s yard; the facility is still being investigated to reconstruct the story of what happened there.

How did such an abusive system endure for 231 years in Ireland? To start with, any talk of harsh treatment at the Magdalene laundries and mothers’ homes tended to be dismissed by the public, since the institutions were run by religious orders. Survivors who told others what they had been through were often shamed or ignored. Other women were too embarrassed to talk about their past and never told anyone about their experiences. Details on both the inmates and their lives are scant.

Estimates of the number of women who went through Irish Magdalene laundries vary, and most religious orders have refused to provide archival information for investigators and historians. Up to 300,000 women are thought to have passed through the laundries in total, at least 10,000 of them since 1922. But despite a large number of survivors, the laundries went unchallenged until the 1990s.

Then, the Sisters of Our Lady of Charity decided to sell some of its land in 1992. They applied to have 133 bodies moved from unmarked graves on the property, but the remains of 155 people were found. When journalists learned that only 75 death certificates existed, startled community members cried out for more information. The nuns explained there had been an administrative error, cremated all of the remains, and reburied them in another mass grave.

The discovery turned the Magdalene laundries from an open secret to front-page news. Suddenly, women began to testify about their experiences at the institutions, and to pressure the Irish government to hold the Catholic Church accountable and to pursue cases with the United Nations for human rights violations. Soon, the UN urged the Vatican to look into the matter, stating that “girls [at the laundries] were deprived of their identity, of education and often of food and essential medicines and were imposed with an obligation of silence and prohibited from having any contact with the outside world.”

As the Catholic Church remained silent, the Irish government released a report that acknowledged extensive government involvement in the laundries and the deep cruelty of the institutions. In 2013, Ireland’s president apologized to the Magdalene women and announced a compensation fund.

Due in part to the uproar surrounding the discovery of the mass grave, the last Magdalene laundry finally closed in 1996. Known as the Gloucester Street Laundry, it was home to 40 women, most of them elderly and many with developmental disabilities. Nine had no known relatives; all decided to stay with the nuns.

Although Smith managed to reclaim her own life, she understands the damage that long-term institutionalization can inflict. “My body went into shell shock when I went there. When that door closed, my life was over,” Smith recalled in her oral history. “You see all these women there and you know you’re going to end up like them and be psychologically damaged for the rest of your life.”