One World Trade Centre, Lower Manhattan, New York City, New York, United States

• Construction
The symbolic cornerstone of One World Trade Center was laid in a ceremony on July 4, 2004 (with an inscription supposedly by Arthur J. Finkelstein), but further construction work was stalled until 2006 due to disputes over money, security and design. The last major issues were resolved on April 26, 2006, when a deal was struck between developer Larry Silverstein and the Port Authority of New York and New Jersey. The cornerstone was temporarily removed from the site on June 23, 2006. For two months during the summer of 2006, explosives were detonated at the World Trade Center construction site, testing the use of charges to clear bedrock for the building's foundations. On November 18, 2006, 400 cubic yards (310 cubic meters) of concrete were poured onto the foundations, carried by as many as 40 trucks. On December 17, 2006, a ceremony was held in Battery Park City, with members of the public invited to sign a 30-foot (9.1 m) steel beam. This beam, the first to be installed, was welded onto the building's base on December 19, 2006. Afterwards, construction of the foundation and further steel installation commenced, and by the end of 2007, the tower's footings and foundations were nearly complete.
In January 2008, two construction cranes were moved onto the site. The tower's concrete core began rising in the first months of 2008, and had reached street level by May 17. Construction of the base continued through 2009 and was completed by January 2010. That same month, construction of the office floors began, then afterwards the installation of the first glass windows. In May 2010, the Port Authority stated that they were building nearly one floor of the tower per week, and it was projected that 1 WTC would reach 55 stories by the end of 2010. An advanced "cocoon" scaffolding system was installed to protect workers from falling, marking the first time that such a safety system had been installed on a steel structure in the city.
On December 16, 2010, the Port Authority announced that the tower's construction had reached the 52nd floor, rising to over 600 feet (180 m) and marking the halfway point for the tower's steel frame. By September 11, 2011, ten years after the destruction of the original World Trade Center, the tower's steel had reached the 82nd floor, while its concrete flooring had reached the 72nd floor, and glass cladding had reached the 56th floor.