Iron workers gather on the roof of One World Trade center to watch as the final piece of spire is hoisted in place, Friday, May 10, 2013 in New York. The addition of the spire, and its raising of the building’s height to 1,776 feet, would make One World Trade Center the tallest structure in the U.S. and third-tallest in the world. (AP photo/Mark Lennihan)

PHOTOS: One World Trade Center topped

The silver spire topping One World Trade Center has been fully installed on the building's roof, bringing the iconic structure to its full, …