In March 2003, two C.I.A. officials surprised Kyle D. Foggo, then the chief of the agency’s main European supply base, with an unusual request. They wanted his help building secret prisons to hold some of the world’s most threatening terrorists.

Foggo went on to oversee construction of three detention centers, each built to house about a half-dozen detainees, according to former intelligence officials and others briefed on the matter. One jail was on a busy street in Bucharest, Romania. Another was a steel-beam structure at a remote site in Morocco that was apparently never used. The third was outside another former East bloc city. They were designed to appear identical, so prisoners would not know where they were if they were shuttled back and forth. They were kept in isolated cells. The existence of the network of prisons to detain and interrogate Al Qaeda members has long been known, but details about them have been a closely guarded secret. In recent interviews, though, several former intelligence officials have provided a fuller account of how they were built, where they were located and life inside them.