The final pieces of the 408-foot spire were hoisted atop One World Trade Center earlier today. When bolted into place at a later date, the spire will make One World Trade Center the tallest building in the western hemisphere. With the spire as its crown, One World Trade Center soars to a symbolic 1,776 feet in the air – a reference to independence of the U.S. from Britain in the year 1776. The building is slated to officially open for business in 2014. The memorial building sits on ground zero, the site of the World Trade Center Twin Towers, which were destroyed by terrorist attacks on September 11, 2001.