Photos of Ground Zero, then and now
On Thursday, U.S. President Barack Obama visits Ground Zero, where 2,792 people were killed at the World Trade Center on Sept. 11, 2001, after hijacked planes destroyed the 110-story twin towers.
A view of Manhattan Aug. 14, 2000, with the World Trade Center towers, as seen from the Brooklyn borough of New York.FERNANDO LLANO
Hijacked United Airlines Flight 175, which departed from Boston en route for Los Angeles, crashes into the South Tower of the World Trade Towers Sept, 11, 2001. The North Tower is shown burning after American Airlines Flight 11 crashed into the tower at 8:45 a.m.ROBERT CLARK
Fritz Koenig's "The Sphere" outdoor sculpture that once graced the plaza at New York's World Trade Center lies in the wreckage of the twin towers following the Sept. 11, 2001, terrorist attacks, in this file photo taken Sept. 24, 2001.TED WARREN
A group of firefighters walk amid rubble near the base of the destroyed South World Trade Center in New York on September 11, 2001.PETER MORGAN
Then-president George W. Bush, in one of the defining moments of his presidency, addresses rescue workers with retired firefighter Bob Beckwith by his side at the scene of the World Trade Center disaster on September 14, 2001.WIN MCNAMEE
One of the damaged connecting pedestrian walkways of the World Trade Center complex still stands at ground zero in New York Sept. 19, 2001.CAMERON BLOCH
New York Fire fighters battle blazes at Ground Zero at the Wolrd Trade Center disaster site, Sept. 19, 2001.HO
A view from the top of the escalators in the Bankers Trust building show the wreckage of the World Trade Center Sept. 25, 2001 in New York.ERIC FEFERBERG
From left: Then-Progressive Conservative leader Joe Clark, Alliance leader Stockwell Day, NDP leader Alexa McDonough, prime minister Jean Chretien and U.S. ambassador to Canada, Paul Cellucci, take in the devastation at ground zero Sept. 29, 2001.TOM HANSON
New York City firefighters, chanting "bring them home," march through the streets of lower Manhattan Nov. 2, 2001. Hundreds of firefighters broke through police barricades and headed to the World Trade Center disaster site to protest a cutback in personnel searching for bodies.BRAD RICKERBY
New York City Police Department members and recovery workers bow their heads as they surround the remains of a comrade at the World Trade Center disaster site, late March 6, 2002.ROBERT MECEA
An empty, flag-draped stretcher is carried past an honour guard and out of the World Trade Center site during a ceremony 30 May 2002 in New York. The empty stretcher symbolizes all who perished but were not found at the site. The ceremony marked the end of the recovery effort at the site.DOUG KANTER
A firefighter tolls a bell as a tribute to fallen comrades during a ceremony at the World Trade Center site in New York on May 30, 2002. The last official piece of debris was removed, along with a stretcher holding an American flag symbolizing the people who were never found.CHIP EAST
A crowd of people whose family members died in the collapse of the World Trade Towers walk into Ground Zero during a memorial service Sept. 11, 2002.STAN HONDA
Family members and friends of those killed gather during the commemoration ceremony of the Sept. 11 attacks at the World Trade Center site in New York Sept. 11, 2003.GREGORY BULL
A man wearing a Boston Police jacket lays a rose into a small pool shortly before the commemoration ceremony at the World Trade Center Sept. 11, 2003.POOL
A model of the future World Trade Center developement sits in front of the Ground Zero construction site in September 2007.EMMANUEL DUNAND
A 'Tribute in Light' illuminates the night sky over lower Manhattan near Ground Zero at the World Trade Center site Sept. 11 2007.TIMOTHY A. CLARY
The World Trade Center "Survivors' Stairs" is moved to its final location at the Memorial Museum site located at Ground Zero Dec. 11, 2008. The stairs are the sole remaining above-ground remnant of the World Trade Center and were used as a key route to safety by those fleeing the terrorist attacks.Mario Tama
Work continues on the concrete core of 1 World Trade Center, the Freedom Tower, which is being constructed at Ground Zero on Dec. 9, 2008 in New York City.Mario Tama
People gather on the roof of a parking garage near Ground Zero to view the 'Tribute in Light' on the eighth anniversary of the Sept. 11, 2001 terrorist attacks on Sept. 11, 2009Spencer Platt
Construction cranes tower above One World Trade Center, Aug. 13, 2010.Mark Lennihan
People celebrate at Ground Zero May. 2, 2011 after President Barack Obama announced hours earlier that Osama bin Laden was killed in an operation led by the United States.Santiago Lyon
With the new One World Trade Center building in the background, second left, a large, jubilant crowd reacts to the news of Osama bin Laden's death at the corner of Church and Vesey Streets, adjacent to ground zero, during the early morning hours of May 2, 2011.Jason DeCrow
Herman Maisonave, of the Queens borough of New York, holds up a sign as he joins those gathered by ground zero in New York as they react to the news of Osama Bin Laden's death early May 2, 2011.Tina Fineberg
A man kisses his child during a visit to Ground Zero after the death of Osama bin Laden on May 2, 2011Michael Loccisano
President Barack Obama speaks to firefighters and first responders at Engine 54, Ladder 4, Battalion 9 before visiting the National Sept. 11 Memorial at Ground Zero in New York, Thursday, May 5, 2011.
U.S. President Barack Obama carries a wreath accompanied by New York City firefighters and police officers during a visit to the World Trade Center site in New York, May 5, 2011.KEVIN LAMARQUE