This article was produced in partnership with the Pulitzer Center on Crisis Reporting.

GUANTÁNAMO BAY, Cuba — Holding the Nazi war criminal Rudolf Hess as the lone prisoner in Germany’s Spandau Prison in 1985 cost an estimated $1.5 million in today’s dollars. The per-prisoner bill in 2012 at the “supermax” facility in Colorado, home to some of the highest-risk prisoners in the United States, was $78,000.

Then there is Guantánamo Bay, where the expense now works out to about $13 million for each of the 40 prisoners being held there.

According to a tally by The New York Times, the total cost last year of holding the prisoners — including the men accused of plotting the Sept. 11, 2001, attacks — paying for the troops who guard them, running the war court and doing related construction, exceeded $540 million.

The $13 million per prisoner cost almost certainly makes Guantánamo the world’s most expensive detention program. And nearly 18 years after the George W. Bush administration took a crude compound called Camp X-Ray and hastily established it as a holding station for enemy fighters picked up in the war on terrorism, it has taken on a sprawling and permanent feel, with the expense most likely to continue far into the future.