The first office tower at Ground Zero since the September 11, 2001 attacks that destroyed the World Trade Center will open on Wednesday, marking a comeback for the Lower Manhattan site.

Sheathed in glass, 4 World Trade Center is the smallest of the four main towers on the site where 2,700 people died when hijacked airplanes crashed into the towers. It stands 977 feet tall - a shorter, simpler version of One World Trade Center, which will not be completed until early 2014.

The 72-story building stands empty at the moment, although two government agencies have signed leases for half of the building's space. Both the Port Authority of New York and New Jersey, which owns the site, and the city of New York committed to the space years ago to help jump start rebuilding efforts.

Since the attacks, disagreements among New York City, the state, the federal government, developers, insurers, victims' families and others have slowed construction on the 16-acre site. Developer Larry Silverstein, who held the lease to the site when it was attacked in 2001, has played a key role in shaping the project's design, security and cost.