"This project is much more than steel and concrete - it is a symbol of success for the nation," said David Samson, chairman of the Port Authority, the agency that owns the World Trade Center.
Clear skies afforded an immaculate 360-degree view from the top, although it wasn't easy getting up there. After riding an elevator to the 90th floor, a small group of officials and journalists had to climb three steep ladders to reach the top platform, which was encircled by blue netting along the perimeter.
The milestone is a preliminary one. Workers are still adding floors to the building once called the Freedom Tower. It isn't expected to reach its full height for at least another year, at which point it is likely to be declared the tallest building in the U.S., and third tallest in the world.
Those bragging rights, though, will carry an asterisk.
Crowning the world's tallest buildings is a little like picking the heavyweight champion in boxing. There is often disagreement about who deserves the belt.
In this case, the issue involves the 408-foot-tall needle that will sit on the tower's roof.
Count it, and the World Trade Center is back on top. Otherwise, it will have to settle for No. 2, after the Willis Tower in Chicago.
Experts and architects have long disagreed about where to stop measuring super-tall buildings outfitted with masts, spires and antennas that extend far above the roof.
Consider the case of the Empire State Building: Measured from the sidewalk to the tip of its needle-like antenna, the granddaddy of all skyscrapers actually stands 1,454 feet high, well above the mark reached by One World Trade Center on Monday.
Purists, though, say antennas shouldn't count when determining building height.
An antenna, they say, is more like furniture than a piece of architecture. Like a chair sitting on a rooftop, an antenna can be attached or removed. The Empire State Building didn't even get its distinctive antenna until 1952. The record books, as the argument goes, shouldn't change every time someone installs a new satellite dish.
Excluding the antenna brings the Empire State Building's total height to 1,250 feet. That was still high enough to make the skyscraper the world's tallest from 1931 until 1972.
From that height, the Empire State seems to tower over the second tallest completed building in New York, the Bank of America Tower.
Yet, in many record books, the two skyscrapers are separated by just 50 feet.
That's because the tall, thin mast on top of the Bank of America building isn't an antenna but a decorative spire.
Unlike antennas, record-keepers like spires. Groups like the Council on Tall Buildings, and Emporis, a building data provider in Germany, both count spires when measuring the total height of a building, even if that spire happens to look exactly like an antenna.