I first visited the prison camp at Guantánamo Bay in April 2003. The “war on terror” prisoners, most of them captured in Afghanistan, had begun to arrive 15 months earlier. They were first locked up in Camp X-Ray, an outdoor prison that looked like a kennel complex for very large dogs. (The police dogs at Camp X-Ray, in fact, had their own cages—the ones without a funnel in the corner for urine.) By the time I arrived, Camp X-Ray had been replaced by Camp Delta; the wire cages had given way to what looked like a heavy-duty, high-security trailer park. The prison cells at Camp Delta were made of shipping containers, sliced in half the long way so that a corridor could be added down the middle, then re-assembled into a kind of grim double-wide. Windows were cut out and fitted with heavy mesh; bugs could penetrate, but not the ubiquitous banana rats, and at least the prisoners didn’t get soaked when it rained.

The prison population peaked that year at 684. But even as the count began to decline, a feeling of permanence took hold. By 2006, Camps 5 and 6 had been built. These were the real thing, copies of high-security facilities in Indiana and Michigan, with electronically controlled gates, central video monitoring of each cell, one-way glass everywhere, and cramped exercise pens. Camps 5 and 6 are where almost all of the remaining prisoners are now kept.

Throughout modern history, governments have used islands for imprisonment or exile. South Africa had Robben Island. Russia had Sakhalin Island. France had Devil’s Island. Guantánamo’s location does not set it apart—nor does the use of physical torture, or the prevalence of hunger strikes, or the nefarious reputation. What is new about Guantánamo has become clear only recently. Rear Admiral Richard W. Butler, who headed up the prison camp until last July, unwittingly alluded to it during my most recent visit earlier in the year. “Twelve years ago,” he said, gesturing to his desk chair, “none of us thought that anybody would still be sitting here today.”

The Bush Doctrine redefined war as something that might go on forever. It created a permanent state of exception, in which extraordinary means were permitted to pursue terrorists (wherever they may be) and to detain suspects (for any length of time). What this has meant for prisoners at Guantánamo is, on one level, well known: without prospect of trial or tribunal, their sentences are effectively open-ended. On another level, what this has meant has never been fully acknowledged. Many of the Guantánamo prisoners are being held in solitary confinement, a difficult condition under the best of circumstances, and psychologically excruciating when no concluding point is specified. Two centuries ago, America was a pioneer in the use of punitive isolation. Now it is pioneering a refinement: the use of solitary without end.

* * *

Joint Task Force Guantánamo, which runs the prison camp at Guantánamo Bay, does not and will not disclose how many of the prisoners in its custody are kept in solitary confinement. The Joint Task Force will not even use the term “solitary confinement,” referring instead to “single-cell operations.” Lawyers and others who work for Guantánamo detainees estimate that from 20 to several dozen of the 127 prisoners still in the prison camp wear the orange jumpsuit of the noncompliant prisoner and are not allowed to eat, exercise, or share space with other prisoners—which is any reasonable person’s definition of solitary confinement.

The military makes solitary confinement very hard to see. In Camp 6, a visitor is allowed to peer, voyeur-like, through one-way glass into one of several blocks that make up the building. It’s like observing the human version of an ant farm. You will see five or six men inside, in white prison uniforms, sitting at metal tables bolted to the floor in a small common area surrounded on three sides by two tiers of cells. The cells are where the prisoners spend the night. Many people are familiar with this kind of prison design from television. When Camp 6 first opened, however, prisoners weren’t allowed to gather in the common area. It was a solitary-confinement unit. Each man was kept in his cell all day long except for a brief period of outdoor exercise, usually at night, alone, in a small space for that purpose attached to the block.