1 World Trade Center spire

On the 20th anniversary of the 9/11 attacks, we look back at the design of One World Trade Center. Controversial nearly every step of the way, from its design to its height, and the political and real estate backstory behind it. One World Trade Center nonetheless paved new ground in terms of designing for security and sustainability in a new century. The building was planned as early as 2003, and construction began in 2006. A 20-ton slab of granite, inscribed with the phrase “the enduring spirit of freedom,” was laid as the cornerstone of One World Trade Center in 2004 by Mayor Michael Bloomberg. The building opened in November 2014. Here are 10 secrets and fun facts about One World Trade Center, an office building, New York City tourist destination and a tribute to those who lost their lives on 9/11.

1. One World Trade Center is the tallest building in the Western Hemisphere

1 World Trade Center

One World Trade Center, previously known as the Freedom Tower, is the tallest building in the U.S. and in the Western Hemisphere, as well as the sixth tallest in the world. The building stands at the symbolic height of 1,776 feet, in honor of the year in which the Declaration of Independence was signed. The height (somewhat controversially) includes its spire, which stands at 408 feet. The building’s architect was David Childs, whose firm Skidmore, Owings & Merrill also designed the tallest building in the world, the Burj Khalifa, as well as the Willis Tower. It is one of only seven supertalls in New York, which are taller than the Empire State Building according to the Skyscraper Museum.

One World Trade Center has an area of 40,000 square feet, nearly identical to the footprints of the original Twin Towers. The tower’s central spire draws from previous buildings such as the Empire State Building and the Chrysler Building. A tall concrete base with a glass-and-steel façade was erected to protect the building from ground-level attacks. Cable-net glass façades line all four sides of the building for higher floors. Above the 20th floor, the building is shaped into eight tall isosceles triangles. The tower forms a perfect octagon near its middle, and then it shifts into a glass parapet. One World Trade Center’s top floor is officially designated as 104, although the tower only contains 94 actual stories. The design of One World Trade Center was by no means the first put out to the public, with a competition for the design long-forgotten.