David Childs

While David Childs, whom Larry Silverstein had hired to design the new tower, appreciated Libeskind’s vision, he also knew he had to make the building architecturally practical. So, he essentially torqued and tapered Libeskind’s design, added more office space, and swapped out the vertical park for a wind-turbine farm (irking environmentalists concerned about errant bird flocks). The building would go through many design modifications, including the squaring and reinforcement of the tower’s base due to NYPD security concerns. In the end, the only feature remaining of Daniel Libeskind’s original concept was the building’s symbolic 1,776-foot height.

With 3.5 million square feet and a price tag of nearly $4 billion, it is still one of the biggest and most expensive office towers ever built.