One World Trade Center Becomes New York City's Tallest Building

New Lower Manhattan tower passes the roof height of the Empire State Building.

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One World Trade Center in Lower Manhattan—previously known as the Freedom Tower—will become the tallest building in New York City on Monday. Standing in one of the world's most iconic skylines, the new building will surpass the roof of the Empire State Building, which stands at 1,250 feet tall, making it the Big Apple's tallest building by some measures.

The Empire State Building is actually 1,454 feet tall counting its 250-foot antenna spire, so One World Trade Center still has a distance to go before it can actually claim the title of the city's tallest building. In the dizzying field of calculating the world's tallest building, a debate has been raging for years about whether the massive antennae that sit atop buildings like the Empire State Building, Chicago's Willis Tower, and New York's Bank of America Tower should count towards the height of the building.

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When completed, the tower will stand at 1,776 feet—including its own 408-foot antenna—making it the tallest building in the Western Hemisphere and the third-tallest building in the world after the United Arab Emirates' Burj Khalifa and Saudi Arabia's Makkah Royal Clock Tower Hotel. The final height was chosen as a symbolic nod to the year the Declaration of Independence was signed.

Following the destruction of the World Trade Center on September 11, plans for a new complex on the site were debated and delayed. After multiple design competitions and revisions to different building proposals, construction on One World Trade Center began in 2006.

The building stands just north of where the "Twin Towers" once stood, a space now occupied by the National September 11 Memorial and Museum. The building includes some characteristic design elements intended to protect it from future terrorist attacks, such as a 185-foot windowless concrete base designed specifically to withstand truck bombs, three-foot reinforced concrete walls in all stairwells and elevator shafts, and a dedicated set of staircases for firefighters.

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Above the concrete base, the building starts to take its shape after the 20th floor. As it rises, eight isosceles triangles built into the building's façade come together to form an perfect octagon near the middle of the tower.

The building is scheduled to reach its final height this spring and will be ready for occupancy in 2013.

Brian Greene writes about politics for U.S. News & World Report. You can contact him at bgreene@usnews.com.