06/25/2012 09:21 am ET Updated Jun 26, 2012

Four World Trade Center Gets Final Steel Beam, Will Open In 2013 (VIDEO)

The final steel beam will be placed atop 4 World Trade Center Monday (weather and lightning-permitting), making it the second of the site's buildings to be completed since September 11, 2001, NBC New York reports. Developer Larry Silverstein will visit the site Monday for a ceremony. The inside of Four World Trade Center is still under construction.

The soon-to-be 977-foot, 72-story tower will be the city's sixth largest skyscraper and will open in the Fall of 2013. Despite its size, at some times of the day, from some angles, it will disappear from the skyline, acting almost as a mirror reflecting the sky. This, says architectural firm Maki and Associates, was intentional. The building, they say, was meant to be subtle, deferential. From The New York Times:

To achieve this effect, the Maki firm designed an especially sheer curtain wall over the steel framework. Glass facades often look cheap because developers will pay only for windows so thin that they bow slightly, creating a quilted effect. The thicker the glass, the flatter the plane of the facade. “It’s not absolutely perfect,” [Osamu] Sassa said candidly about the curtain wall at 4 World Trade Center, “but I think we’ve achieved something of high quality.”

4 World Trade Center's completion caps off more than a decade of design, debate and construction at the site. (For a full timeline of the site that's no longer "Ground Zero," go here.)

While President Obama signed a steel beam set to be placed atop One World Trade Center (currently at 104 floors), the final steel beam of Four World Trade Center will be signed by a group of workers.

Correction: This article previously stated that Four World Trade Center would be the first to be completed since the 9/11 attacks. It is the second. Seven World Trade Center, at 52 stories, opened in 2006.