FOR MEMORY: Construction workers sign their names on the final steel beam of Four World Trade Center in New York City on June 25 (HUANG WEI)

A crane lifts a steel beam adorned with an American flag and weighing 8 tons 977 feet (around 297.8 meters) in the air and places it atop a 72-story tower in New York City's Lower Manhattan.

Approximately 1,000 construction workers and other city leaders attended the topping out ceremony on June 25, marking the end of steel construction on Four World Trade Center. Workers signed the final beam before raising it, as is customary in topping out ceremonies for skyscrapers. It will be the first office tower to be completed and opened on the 16-acre site since the events of September 11.

"The topping out of Four World Trade Center represents another milestone in the effort to create a new, dynamic World Trade Center at the heart of a resurgent downtown," said property developer Larry A. Silverstein.

"The fundamental approach to the design is two-fold: a minimalist tower that achieves an appropriate presence, quiet but with dignity, becoming a tribute to the memorial, and a podium that becomes a catalyst in activating and enlivening the immediate urban environment as part of the revitalization of downtown New York," said Maki Fumihiko, the Pritzker Prize-winning architect who designed the tower at 150 Greenwich Street.

RAISING HIGH: A crain rases the final beam of Four World Trade Center in New York City on June 25 (HUANG WEI)

The sleek glass and steel office building is reportedly intended as an architectural backdrop to the September 11 Memorial. Seen from a distance, the trapezoidal building nearly disappears at some angles at specific times of day, like a massive mirror reflecting the sky.

"This building is basically like a butterfly just released from the cocoon right now displaying its beautiful colors and the shape and size of this building here. It's a big day for the boys and girls here at tower four," said Frank Hussey, superintendent of Tishman Construction.

More than 1,200 union construction workers put in over 3 million hours to build the tower. "It now stands as part of the skyline of New York as a testament to their resolve to never give up, always move forward, and build New York bigger, better and stronger," said Gary LaBarbera, president of the Building and Construction Trades Council of Greater New York.

Four World Trade Center is slated to open in the fall of 2013, according to the Port Authority of New Jersey & New York.

(Reporting from New York City)