Solitary confinement as a formal prison practice began in 1829 at Eastern State Penitentiary in Philadelphia, the world’s first true “penitentiary.” But its roots stretch back centuries earlier, to the isolation cells of Christian monasteries. Understanding that lineage helps explain why solitary confinement was created, why it persisted despite early evidence of harm, and how it evolved into the practice still used in prisons today.
The Monastic Cell Came First
Long before prisons adopted isolation as punishment, monks used it as spiritual discipline. Christian monastic traditions treated solitude as a path to repentance and inner transformation. A monk who had sinned might be confined alone to reflect, pray, and emerge spiritually renewed. This idea, that forced solitude could change a person’s soul, became deeply embedded in Western thinking about punishment.
As one Princeton University history of solitary confinement puts it, the prison cell is “the weaponization of the monastic cell.” The logic carried directly from monastery to penitentiary: if isolation could produce spiritual rebirth for monks, perhaps it could produce moral rebirth for criminals. That theological conviction, that souls can be changed “by force if necessary,” shaped centuries of penal policy.
Eastern State Penitentiary and the Pennsylvania System
In 1821, a group of Philadelphia prison reformers, many of them Quakers, convinced the Pennsylvania Legislature to build a new kind of prison on elevated land northwest of the city, in what is now the Fairmount neighborhood. They chose the hilltop site partly because they believed clean airflow away from the polluted industrial center would produce healthier prisoners. Eastern State Penitentiary opened in 1829 and introduced what became known as the “Pennsylvania model” of imprisonment.
Under this system, every prisoner lived in 24-hour solitary confinement. Each inmate occupied an individual cell with a small private exercise yard, saw no other prisoners, and worked alone at solitary crafts. The goal was not to inflict suffering, at least not in the eyes of its creators. Reformers designed the system to “mentally break prisoners and inspire true regret in their hearts,” replacing the physical punishments common at the time (flogging, branding, public humiliation) with what they considered a humane alternative. The very word “penitentiary” comes from “penitence,” the religious concept of sorrowful reflection that the system was built around.
Eastern State became internationally famous. Visitors from across Europe toured its radial cellblocks. Charles Dickens visited in 1842 and left horrified, writing that the psychological damage he witnessed was worse than any physical torture.
The Auburn System Won Out
Almost immediately, a competing model emerged. New York’s Auburn Prison developed a system where inmates were still isolated at night but worked together in silence during the day, in factory-style workshops. This “Auburn system” was a deliberate compromise: it kept the isolation and silence that reformers valued while allowing the kind of group labor that generated revenue.
By the mid-1800s, the Auburn model had displaced the Pennsylvania system across most of the United States, and the reason was largely economic. When prisoners worked together in a factory setting, their output was dramatically more profitable than the solitary crafts performed in Pennsylvania-style cells. Prison officials were willing to compromise their reform-minded intentions to maximize the efficiency of prison labor and create a system that paid for itself. The de facto goal at Auburn-style prisons like New York’s Sing Sing became profit, not penitence.
This shift didn’t end solitary confinement. It simply changed its role. Instead of being the default condition for every prisoner, isolation became a tool of punishment within prisons, reserved for rule-breakers and those deemed dangerous.
Early Evidence of Psychological Harm
The damage caused by prolonged isolation was documented remarkably early. By the late 1800s, reports from Pennsylvania-style prisons showed devastating outcomes: a considerable number of prisoners fell into a near-catatonic state after even short periods of confinement, others became violently insane, and some committed suicide. Those who endured the ordeal without a complete breakdown still suffered lasting cognitive damage, never recovering enough mental function to reintegrate into society.
In 1890, the U.S. Supreme Court acknowledged these findings in a case called In re Medley. The Court didn’t ban solitary confinement outright, but the justices described its effects in stark terms, citing the mental deterioration, psychosis, and suicides that isolation produced. Despite this early judicial recognition, the practice continued with little restriction for more than a century.
The Supermax Era
Solitary confinement’s modern expansion began with a specific crisis. In 1983, two prison guards were murdered at the Marion Federal Penitentiary in Illinois. In response, the facility placed all 350 inmates on indefinite “lockdown,” confining them to their cells for 23.5 hours per day and suspending visits. The lockdown was never fully lifted. Marion became the template for a new kind of facility: the supermax prison, designed from the ground up for permanent or near-permanent isolation.
Through the 1990s and 2000s, supermax prisons proliferated across the country. States built dedicated facilities where inmates spent 22 to 24 hours a day alone in small cells, sometimes for years or even decades. What had begun in 1829 as a Quaker experiment in moral reformation had become a widespread tool of prison management, applied not just to the most dangerous inmates but also to those with mental illness, gang affiliations, or disciplinary infractions.
Where Solitary Confinement Stands Today
As of late 2024, roughly 12,000 people were held in restrictive housing across all federal prisons in the United States, according to the Government Accountability Office. That number doesn’t include the far larger population in state and local facilities, where estimates have historically run much higher.
International standards now define solitary confinement as confining a prisoner for 22 hours or more per day without meaningful human contact. The United Nations’ Mandela Rules, updated in 2015, state that any solitary confinement beyond 15 consecutive days constitutes a form of torture. Placing people with mental or physical disabilities in solitary confinement is prohibited under international law entirely.
Some states have begun passing legislation to limit the practice. New York’s HALT Act, signed into law in March 2021, caps the length of time a person can spend in segregated confinement, restricts which offenses can lead to isolation, and exempts vulnerable populations. The law also requires prisons to use the least restrictive environment necessary and to create residential rehabilitation units offering therapy and programming as alternatives. Other states have pursued similar reforms, though implementation remains uneven.
The GAO has noted that federal prisons have not adequately addressed longstanding concerns about overuse of solitary confinement, suggesting the gap between policy goals and daily practice remains wide. Nearly two centuries after Eastern State Penitentiary opened its doors, the tension between isolation as a tool of control and its well-documented psychological costs is still unresolved.