With the blast of an airhorn, ironworkers on Monday began bolting into place the first of 610 steel pieces of the soaring wing-like arches of the World Trade Center's new transportation hub.
Not due to open until 2015, the 800,000-square-foot (74,322-square-meter) transit hub will eventually link numerous New York City subway lines with commuter trains and ferry services to neighboring New Jersey.
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One official called the rising of the arches a "significant milestone" in the rebuilding of the World Trade Center complex, which was destroyed by hijacked airliners on September 11, 2001, killing nearly 3,000 people.
"We will not, at this site, allow us to be defined as a people by those events," said Steve Plate, director of construction for the Port Authority of New York & New Jersey, which owns the World Trade Center site.
Although the Port Authority has pared back some aspects of Spanish architect Santiago Calatrava's design, including fixing in place the steel-and-glass arches that were once intended to be retractable, the cost of the project has almost doubled from its original estimate to nearly $4 billion.
Calatrava has said his design was intended to evoke a white dove taking flight.
PATH commuter trains have been running in and out of the site since shortly after the attacks with a makeshift entrance at the surface. Beset by years of delays, the rebuilt World Trade Center site is taking form.
The National September 11 Memorial, constructed around the footprints of the fallen twin towers, opened on the 10th anniversary of the attacks in 2011, although the accompanying museum is still under construction.
Workers last week moved into place the final pieces of the spire atop One World Trade Center, the site's tallest skyscraper, which when completed, will reach 1,776 feet.