For 13 years, Americans have waited for the day when the World Trade Center would rise again as a symbol of New York City's resilience in the wake of the 9/11 terror attacks. That day has finally come, as employees of publisher Condé Nast began to move into the new One World Trade Center building Monday morning, bringing commerce back to a site that has long stood lifeless, a reminder of the nearly 3,000 lives that were lost on Sept. 11, 2001.

The opening of the glistening One World Trade Center tower (still called by many the Freedom Tower after its original proposed name) in Lower Manhattan's Financial District is taking place in stages. Condé Nast will not be finished moving its employees from the Condé Nast Building on Times Square until February, but a formal grand opening is expected by year's end, the New York Times reported Monday.

"One World Trade Center serves as a symbol of the resilience of the people of New York,” New York Gov. Andrew Cuomo said in a statement. “Today, as we open its doors for the first time, we remember that strength and courage will always conquer weakness and cowardice, and that the American spirit, defended by proud New Yorkers, will not be defeated.”

The $3.9 billion, 104-story One World Trade Center building is not only America's tallest building, but a potent reminder of the 9/11 terror attacks and the strides New York City has made in recovering since that day. "The New York City skyline is whole again," Patrick Foye, executive director of the Port Authority of New York and New Jersey -- owner of the WTC site -- said in a statement.

Condé Nast, a division of the Newhouse family-owned Advance Publications, holds a special place in the history and future of One World Trade Center. The company signed on as the building's first "anchor tenant," announcing in 2011 that it would move to the building in a move that prompted a wave of interest in the property.

Only 170 of the company's 3,400 employees are moving into the building Monday, according to Condé Nast vice president and spokeswoman Patricia Rockenwagner, while about 3,000 more workers are expected to settle there by early 2015, CBS New York reported. The company said it is “proud to be a part of this important moment of renewal for the city,” according to the New York Times.

One World Trade Center is 60 percent leased, while New York City's General Services Administration has reserved 275,000 square feet, according to the BBC.