NEW YORK — Al-Qaida has long had a fascination with suspension bridges, especially the Brooklyn Bridge. New documents reveal that before Sept. 11, 2001, methods for bringing down bridges were being taught at a terrorist training camp in Afghanistan.

After 9/11, Khalid Sheikh Mohammed, the admitted mastermind of the attacks, got even more specific, telling an operative, Iyman Faris, to "destroy the Brooklyn Bridge by cutting the suspension cables," according to a 2006 assessment of Mohammed that is among the hundreds of classified Guantanamo files made available recently to The New York Times.

The Brooklyn Bridge plot was revealed in 2003 with the arrest of Faris, a naturalized U.S. citizen from Kashmir.

But the brief reference in the report on Mohammed hints at the impact of the aborted plot on security in New York and on the bridge in particular. Today, the bridge is one of the most carefully guarded potential targets in New York — maintenance crews, for example, must notify the Police Department's Intelligence Division before scaling the cables.

Security cameras watch hidden corners of the bridge. Other measures, like police cars stationed on entry ramps, are there for all to see. To at least some extent, that is the legacy of the plot, no matter how far-fetched it might have seemed at the time.

In fact, the Police Department realized it was not far-fetched at all. After Faris' arrest, Police Commissioner Raymond W. Kelly visited an isolated room near where the thick cables split into several thinner cables and are anchored on the shore. A vulnerability, he said, had been detected.

"I, myself, climbed down and looked at the room where the cables came together, after the Faris plot," Kelly said. Someone could enter that room, he said, and "cut or physically weaken the center cables of the bridge."

"If you look through all the components of it," he added, "it was doable."

The newly revealed Guantanamo assessments, obtained last year by the group WikiLeaks and provided by another source to The Times, show that those who mentioned bridges as possible targets were among the most high-profile al-Qaida operatives, like Mohammed and Abu Zubaydah.

An assessment of Zubaydah says he provided interrogators with a list of potential al-Qaida targets, including "U.S. symbols" like the Statue of Liberty, the U.N. building and "major hanging bridges," the report says.

It was an Egyptian detainee named Tariq Mahmoud Ahmed al Sawah who told interrogators about a course in improvised explosive devices given at the training camp, where he learned about "methods to destroy suspension bridges," his assessment says.

References to the Brooklyn Bridge were being picked up by intelligence officers in the Police Department before 9/11. Images of the bridge appeared, for example, in the backgrounds of prerecorded memorial messages left behind by suicide attackers overseas. After 9/11, said Paul J. Browne, the chief police spokesman, the department hired an engineer to study the ways the bridge could be taken down.

Karen J. Greenberg, executive director of the Center on Law and Security at New York University, said the reference to the Brooklyn Bridge in Mohammed's file underscored the bridge's importance as a target — as a symbol and because of the potential "for disrupting the commercial fabric of the city."

"You get a sense from these of how al-Qaida was thinking," Greenberg said. "It's akin to blocking the port in a way. It's a major point of entry."

In addition to the police cars on the ramps, a police boat is always nearby in the East River, with officers keeping their eyes on the bridge. Those measures were put into place after 9/11, and Kelly has said he believed they deterred Faris.