THEN AND NOW: How New York City's World Trade Center has changed in the 15 years since the 9/11 terrorist attack

The ‘Twin Towers’ of the World Trade Centre under construction, circa 1971.
Photo: Paul Popper/Popperfoto/Getty Images

Completed in 1973, the original World Trade Center complex was dubbed a “dream come true” by Governor Nelson Rockefeller at the official ribbon cutting ceremony on April 4.

After the September 11, 2011 terrorist attacks left a hole in New York’s skyline, ideas started spewing about what and how to rebuild.

Years later, One World Trade stands in its place. It’s not just the Western Hemisphere’s tallest building — it has also become a symbol of American pride.

See how the original World Trade Center evolved into today’s Freedom Tower after the attacks of 9/11.

Upon completion in 1973, the towers stood as the world's tallest buildings at 1,368 feet tall. The Willis Tower, formerly known as the Sears Tower, stole the title in 1974 at 1,451 feet tall.

The Twin Towers in 1974. Photo: Peter Keegan/Keystone/Getty Images

Source: New York State Education Department, History.com

As their popularity increased, the Port Authority created the Windows on the World restaurant on the North Tower's 107 floor. Opened in April 1976, the restaurant delivered aerial city views to diners.

Restaurant interior. Photo: Wikimedia Commons. Licensed under Creative Commons 3.0.

Source: New York State Education Department, History.com

Today, One World Trade Center -- or the Freedom Tower, as it's known by many -- represents national strength, pride, and America's ability to rebuild.

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Construction began in 2006 and was completed in 2014. In 2012, The Wall Street Journal reported the building's budget rose to $3.8 billion, making it the world's most expensive new office tower at the time.

Screenshot via NBC News

Source: The Wall Street Journal

The 104-story tower is constructed with more than 2,000 pieces of prismatic glass and stands at 1,776 feet tall. Its height is a subtle tribute to the year America declared its independence.

Brittany Fowler/Business Insider

Source: World Trade Center

The One World Observatory officially opened to the public on May 29, 2015. The observatory sits 1,250 feet above the city, providing visitors with unique views, just as Windows on the World had done nearly four decades before.

Brittany Fowler/Business Insider

Source: World Trade Center

The observatory's elevators -- called 'skypods' -- have animated interiors that show New York City's construction throughout history. It only takes 60 seconds to reach the top.

Brittany Fowler/Business Insider

Source: World Trade Center

Visitors are guided through media-walled rooms that discuss the construction of One World Trade before reaching the skypods. Manhattan schist, a type of granite, serves as the building's foundation, and it's 450 million years old.

Brittany Fowler/Business Insider

Source: World Trade Center, 911memorial.org

Today, the site is also home to the National September 11 Memorial and Museum. Names of the nearly 3,000 people who died in the September 11 attacks, in addition to those who died in the 1993 bombing, are inscribed in the bronze panels that border the pools.

Brittany Fowler/Business Insider

Source: 911memorial.org

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