NEW YORK – Lower Manhattan again will dominate the skyline Monday as the World Trade Center reclaims its place as the city's tallest structure.

The milestone is a major step in the symbolic recovery of New York -- and the nation. One World Trade Center replaces the Empire State Building, which has held the tallest building designation since the terror attacks of Sept. 11, 2001, destroyed the Twin Towers.

At 3:30 p.m., workers installed the first column of the 100th floor, bringing the height of One World Trade Center to 1,271 feet. The tower is to be topped off this summer.

When completed at a patriotic 1,776 feet and 104 floors, the so-called Freedom Tower will be 408 feet taller than the twin towers, according to the Chicago-based Council on Tall Buildings and Urban Habitat, a not-for-profit group that tracks the building industry.

One World Trade Center would surpass the 1,451-foot Willis Tower (former Sears Tower) in Chicago to become the tallest in the Western Hemisphere, says council spokesman Kevin Brass. The world's tallest building is the Burj Khalifa in Dubai, at 2,717 feet.

The new building towers over a neighborhood that is bustling anew.

When it was the pinnacle of American and global finance in the days of the Twin Towers, lower Manhattan all but shut down by 5 p.m. each day and slept through the weekends. Today, the redeveloped area is bustling 24-7.

The neighborhood has become something of a "Times Square South," full of tourists, retail, new apartment complexes and, yes, even a thriving nightlife -- not to mention the Occupy Wall Street movement.

Before the Sept. 11 attacks, the center's Twin Towers were home to such financial powerhouses as Morgan Stanley and Canter Fitzgerald. The new tenants are an eclectic mix.

The Conde Naste media company will be the biggest tenant in One World Trade Center.

"We all couldn't be happier," said Peter Davidson, executive director of the Empire State Development Corp. and board member of the Lower Manhattan Devlopment Corp., which was charged with revitalizing the neighborhood after the attacks.

"It's a hip and cutting-edge tenant," he said of Conde Naste. "Their workers are young and educated."

Workers in fields outside of finance won't just be filling up office space. They're also moving into the neighborhood.

"Lower Manhattan is the fastest-growing area of New York City in terms of residential construction," Davidson said. "It was the financial center before. That was great, but at 5, it shut down and there was no life after 5."

Now, on places like Stone Street -- a cobblestone side road loaded with bars and restaurants -- the opening bell rings at 5 p.m.

The neighborhood is expected to gel over the next couple of years, especially when the ESDC completes a $3 billion transit hub at the trade center and the $400 million World Trade Center Museum opens for an expected 3 million to 5 million tourists a year.

One World Trade Center's ultimate height doesn't come without controversy: its 1,776 feet includes a 408-foot-tall needle on the roof. Experts disagree on where to stop measuring monoliths outfitted with antennas, spires and masts. Purists say anything that can be removed, such as an antenna, should not be counted.

"Height is complicated," said Nathaniel Hollister, a spokesman for The Council on Tall Buildings and Urban Habitats, a Chicago-based organization considered an authority on such records.

The Empire State Building has an antenna, too, added in 1952. Counting the antenna, the granddaddy of super-tall skyscrapers stands 1,454 feet, well above the mark being surpassed by One World Trade Center on Monday.

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 super-tall skyscrapers actually stands 1,454 feet high, well above the mark being surpassed 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. It's a tradition that harkens back to a time when the tallest buildings in many European cities were cathedrals. 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.

This quirk in the record books has benefited buildings like Chicago's recently opened Trump International Hotel and Tower. It is routinely listed as being between 119 to 139 feet taller than the Empire State Building, thanks to the antenna-like mast that sits on its roof, even though the average person, looking at the two buildings side by side, would probably judge the New York skyscraper to be taller.

Construction of One World Trade Center won't be completed until fourth quarter 2013 or first quarter 2014, Foye says. He says the structure is about 55% leased and is "poised to be a commercial success."

News of the tower claiming top spot in the city's skyline is a bright spot for a redevelopment project plagued by cost overruns and delays .

An audit found that World Trade Center redevelopment costs grew from an estimated $11 billion in 2008 to $14.8 billion today.