Mark Lennihan/AP Photo

A steel beam signed by Obama being installed at One World Trade Center on Thursday.

A steel beam signed by President Obama was installed today on the 104^th floor of One World Trade Center, the skyscraper being built to replace the towers destroyed on September 11, 2001.

The beam was signed during a visit to the construction site last month and inscribed with the words, "We remember/We rebuild/We come back stronger!" First lady Michelle Obama, New York City Mayor Michael Bloomberg and Governors Andrew Cuomo and Chris Christie also added their signatures along with construction workers and police officers.

The 35-foot long, 11,000lb beam will no longer be visible as it's sealed into the tower as construction continues.

Mark Lennihan/Associated Press

One World Trade Center changing the shape of the New York City skyline (file).

Today, a day before the one-year anniversary of the killing of Osama bin Laden, One World Trade Center became the tallest building in New York City.  Nearly 11 years after the terrorist attacks on September 11, 2001,  One World Trade Center inched it's way past the Empire State Building when a column on the 100th floor was installed earlier today.

When completed, One World Trade Center will have a total of 104 floors, and be 1,776 feet high including the antenna.  At that height (antenna included) the office building will be taller than the Willis Tower in Chicago, making it the tallest building in the United States. After years spent in legal purgatory, the 9/11 memorial project and new office skyscraper are finally reaching their completion. Currently, progess at the site has seen one floor built per week. The building will have 69 floors dedicated to office space and will include an observation deck overlooking lower Manhattan.

Today's milestone was marked quietly as construction at the site continues, but with the memorial site including the two reflecting pools in the footprint of the original Twin Towers now open to the public - the constant construction at the site of the worst terrorist attack in this country's history is finally coming to an end. One World Trade Center is expected to open in the Spring of 2013.