Work to redevelop the site of New York's World Trade Center is under way, a day after an agreement was reached ending a four-year deadlock.
Five towers will be built on Ground Zero by 2012
New York officials applauded workers as they arrived at the construction site.
The centrepiece Freedom Tower will be the United States' tallest building and fill the hole left in the city's skyline by the 9/11 terrorist attacks.
The deal agreed by site landlord Larry Silverstein was passed by the city's Port Authority, which owns the site.
New York governor George Pataki, New Jersey governor Jon Corzine, New York Mayor Michael Bloomberg and Mr Silverstein were on site on Thursday as the excavation trucks rolled in.
"It is going to be a symbol of our freedom and our independence," Mr Pataki said, referring to the Freedom Tower which will rise 1,776 feet (540m).
"We are not going to just build low in the face of a war against terror. We are going to soar to new heights and reclaim the New York skyline," he said.
Wednesday's agreement ended years of often acrimonious talks over the proposed redevelopment between multi-millionaire developer Mr Silverstein and port and city officials.
Larry Silverstein has clashed with city officials over the plans
At every step, there have been disagreements over the design, financing and even ownership of the proposed redevelopment on Ground Zero.
Under the deal, Mr Silverstein will build four of the five skyscrapers planned for the site, including the Freedom Tower. The Port Authority of New York and New Jersey will build the fifth building.
Upon completion, Mr Silverstein will hand over control of the Freedom Tower and one other building to the Port Authority.
Officials say the deal means they are on course to finish the buildings by 2012.
Mr Silverstein signed a 99-year lease on the World Trade Center less than two months before the 11 September 2001 attacks.
He was awarded $4.6bn in insurance money after the collapse of the Twin Towers.
Neither side could agree on who would build on Ground Zero, how much rent would be paid, and how to divide the money paid to Mr Silverstein after 9/11.
When talks again broke down in mid-March, Port Authority officials angrily accused Mr Silverstein of negotiating in bad faith.
Mr Silverstein insisted rebuilding the site was the most important thing in his life.