Thirteen years after the 9/11 terrorist attack, the revived World Trade Center is again opening for business. It marks an emotional milestone for the United States.

Publishing giant Conde Nast will start moving on Monday into One World Trade Center, a 104-story, $3.9 billion skyscraper dominating the Manhattan skyline. It is America’s tallest building!

Patrick Foye, executive director of the Port Authority of New York and New Jersey that owns both the building and the World Trade Center site, says the building is whole again.

“The New York City skyline is whole again, as One World Trade Center takes its place in Lower Manhattan. It sets new standards of design, construction, prestige and sustainability; the opening of this iconic building is a major milestone in the transformation of Lower Manhattan into a thriving 24/7 neighborhood.”

Only about 170 of his company’s 3,400 employees are moving in at the moment, filling five floors, according to Patricia Rockenwagner, a Conde Nast vice president and spokeswoman.

About 3,000 more is expected to arrive by early 2015.