The Survivors' Staircase forms the centrepiece of the exhibition of artefacts recovered from the World Trade Center.
A staircase used by hundreds of survivors as they fled the ruins of the World Trade Center during the 9/11 attacks has gone on show at New York's National September 11 Memorial & Museum, ahead of the venue's official opening next spring.
A huge, dented piece of the building's facade, which bore the brunt of the impact of Flight 11 as it slammed into the Trace Center's North Tower, stands alongside it at the exhibition, which is being held in honour of the 2,996 people who died that day.
Mangled pieces of steel recovered from the burned out wreck of the structure after the attack include the two vast steel columns that originally rose from the base of the North Tower.
Visitors enter to be confronted by the two rusted red columns as they rise into the glass atrium that houses the museum entrance.
Joseph Daniels, president of the memorial and museum, said: "They're so large - about 70ft tall - that we built the museum around them.
"You can see how, at the bottom, the columns are bent back. That's because Flight 11's nose, when it pierced the building, bent steel like that."
'We are all survivors'
But it is the Survivors' Staircase that is acknowledged as the museum's most haunting exhibit.
Museum director Alice Greenwald said: "You're literally following the same pathway that hundreds followed on 9/11 to survival, to safety.
"In some respects, what we're saying to our visitors is, we all live in a world now that was defined by this event. And in that sense, we're all survivors of 9/11."
Four passenger airliners were hijacked on 11 September 2001 by 19 al-Qaida terrorists. American Airlines Flight 11 and United Airlines Flight 175 flew directly into the North and South Towers of the World Trade Center complex.
Both towers collapsed within hours.
A third plane, American Airlines Flight 77, crashed into the Pentagon in Washington, the headquarters of the US Defense Department, while a fourth, United Airlines Flight 93, is thought to have been bound for Capitol Hill in Washington, home to the US Congress, but crashed into a field near Shanksville, Pennsylvania after its hijackers were overpowered by passengers.
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