From Ground Zero to the Freedom Tower?

World Trade Center towers, 2000
On April 4, 1973 the New York City skyline dramatically changed. It was on that day, 40 years ago, that the original World Trade Center site officially opened. The Twin Towers, seen here in 2011, were an iconic part of the skyline.

One World Trade Center surpasses Empire State Building, 2012
One World Trade Center eclipsed the Empire State Building as New York's tallest building on April 30, 2012. The tower surpassed the 1,250-foot Empire State Building on its way to a final height of 1,776 feet.

One World Trade Center spire, 2013
This detailed view shows the spire in its entirety atop One World Trade Center on May 10, 2013. "It's basically showing (the terrorists), 'You can't take America down. We'll rebuild,'" said Eddie Fackler, who was meeting a friend downtown on May 10. "It's a sense of who we are."

One World Trade Center spire, 2013
Site construction worker Mike Prender is proud of reaching the milestone: "I think we need it - as a city, as a nation. It's inspiring. It's good for America." Here, iron workers lean out as they watch a crane lift the final piece of the spire into place atop One World Trade Center on May 10, 2013.

One World Trade Center spire, 2013
The 408-foot spire now rests atop One World Trade Center, making the building the tallest in the Western Hemisphere. In the distance, the Empire State Building can be seen.

One World Trade Center, 2013
The spire is the tip top point of One World Trade Center. With the addition of it on May 2, 2013, the stunning tower becomes the tallest building in the Western Hemisphere

One World Trade Center, 2013
With the spire in place, the New York City skyline continues to rebuild itself. Here, One World Trade Center is seen in the backdrop of another Big Apple icon, the Statue of Liberty.

One World Trade Center, 2013
Going up! The flag-draped spire of the new One World Trade Center soared above the city skyline on May 2, 2013 at an emotional ground zero ceremony. Hundreds of construction workers cheered and snapped photos as they watched the tip of the mast make its way to the top of the iconic building.

One World Trade Center, 2012
One World Trade Center, seen here in 2012 from World Trade Center 4, will be the centerpiece of the redeveloped World Trade Center site.

One World Trade Center, 2012
By 2012, One World Trade Center was growing by nearly a floor a week. From the ground, the building looked nearly completed back in March 2012.

One World Trade Center, 2013
Reaching heights of 1,776 feet, One World Trade has surpassed the Empire State Building to become the tallest building in New York City. Previously dubbed the Freedom Tower, the building proudly stands tall in Lower Manhattan as a reminder of the resilience of New York City after a grave act of terror. The installation of the silver spire topping One World Trade Center was finished on May 10, 2013, bringing the iconic structure to its full, symbolic height of 1,776 feet. The final bolts were installed to secure the spire onto the building at 8 a.m., workers said. Follow One World Trade Center's rise from a devastated Ground Zero to the third tallest building in the world ...

One World Trade Center, 2012
When antennas are erected on top of the tower, its height will rise to 1,776 feet. Upon its completion, One World Trade Center will stand as the third tallest building in the world with 104 floors. Here, a crane on the top deck of One World Trade Center lifts a steel beam that makes 1 WTC the tallest skyscraper in NYC.

One World Trade Center, 2011
One World Trade Center has risen to take its place along the New York City skyline. As it rises to its final height of 1,776 feet, it fills the gap in the iconic skyline voided by the 9/11 attacks.

South Pool of the 9/11 Memorial, 2011
Pictured here is the completed South Memorial Reflecting Pool, built on the footprint where the South Tower once stood.

Rendering of the Freedom Tower
Two years later, in 2003, artist renderings were revealed and showed off the Freedom Tower that was slated to rise at the site of the former World Trade Center in Lower Manhattan. The Tower is set to be completed in 2013 and open for business in 2004.

Ground Zero, 2006
Construction at the Ground Zero site began in 2006 after disputes between the Port Authority and the developer. It wouldn't be until 2008 that the building would reach ground level.

Ground Zero, 2001
Two days after the massive terrorist attacks on the World Trade Center, only debris and an American flag could be seen standing at Ground Zero. This Sept. 13, 2001 photo shows the destruction and devastation of the attacks.

Freedom Tower, 2010
The entire Ground Zero site has been reconstructed into multiple World Trade Towers and the National September 11 Memorial & Museum, which is complete with two reflecting pools that stand in place of the downed Twin Towers. The entire construction zone can be seen here in 2010.

Freedom Tower, 2011
Up and away it goes! By 2011, the Freedom Tower soared to great heights. It is slated to become the third tallest building in the world when it reaches 104 floors.

Freedom Tower, 2009
In 2009, construction workers continued to toil away and rebuild the iconic New York City skyline. One World Trade is seen here in Dec. 2009 from the 10th floor of 7 World Trade Center.

Freedom Tower, 2008
Construction on One World Trade broke ground level in 2008. The Freedom Tower began to take shape, as seen in this Sept. 4, 2008 photo.

Freedom Tower, 2006
The northwest corner of Ground Zero looked like this back in 2006 as the very beginnings of the Freedom Tower were constructed.

Cornerstone of the Freedom Tower lifted, 2004
The cornerstone for the Freedom Tower was lifted into place at the base of the Ground Zero site on July 4, 2004. The Independence Day ceremony marked the dedication of the new building, but quarrels between the builders and the Port Authority delayed construction until 2006.

Construction of reflecting pools, 2010
The outlines of the reflecting pools can be seen here in 2010 during mid-construction. The memorial officially opened to the public on Sept. 12, 2011, a day after the 10th anniversary of the 9/11 attacks.

9/11 attacks on the World Trade Center
But even after all that had happened on Sept. 11, firefighters found a way to raise the American flag.

9/11 attacks on the World Trade Center
America - and specifically New York City - were attacked on Sept. 11, 2001. After being hit by two airplanes, the World Trade Center towers crumbled. The devastated area became known as Ground Zero ...