<Dd> a . April 2012 estimate . </Dd> <Dd> b . Skidmore, Owings & Merrill . </Dd> <P> One World Trade Center (also known as 1 World Trade Center, 1 WTC or Freedom Tower) is the main building of the rebuilt World Trade Center complex in Lower Manhattan, New York City . It is the tallest building in the Western Hemisphere, and the sixth - tallest in the world . The supertall structure has the same name as the North Tower of the original World Trade Center, which was destroyed in the terrorist attacks of September 11, 2001 . The new skyscraper stands on the northwest corner of the 16 - acre (6.5 ha) World Trade Center site, on the site of the original 6 World Trade Center . The building is bounded by West Street to the west, Vesey Street to the north, Fulton Street to the south, and Washington Street to the east . </P> <P> The building's architect was David Childs, whose firm Skidmore, Owings & Merrill (SOM) also designed the Burj Khalifa and the Willis Tower . The construction of below - ground utility relocations, footings, and foundations for the new building began on April 27, 2006 . One World Trade Center became the tallest structure in New York City on April 30, 2012, when it surpassed the height of the Empire State Building . The tower's steel structure was topped out on August 30, 2012 . On May 10, 2013, the final component of the skyscraper's spire was installed, making the building, including its spire, reach a total height of 1,776 feet (541 m). Its height in feet is a deliberate reference to the year when the United States Declaration of Independence was signed . The building opened on November 3, 2014; the One World Observatory opened on May 29, 2015 . </P>

What is the name of the tower that replaced the twin towers