There are photographs that one can see of the World Trade Center where from the outside, you look at it and it's a totally opaque object, or objects. And that's particularly the case when the sun was on the facade. With the sun behind, you could see right through the building. It was literally almost transparent, almost transparent. You could look right down through the elevator corridor to the other side of the building. Nothing like that had ever been created before. Before, there were columns that -- relatively close spacing -- 30 feet on center, something like that. And those systems worked pretty well. But the Trade Center had a different kind of structure. It was built more like the wing of an airplane. And the wing of the airplane, the strength is all in the surface of the wing, or the fuselage, on both cases. You can't have columns down through the center of your passenger airplane.

And so the Trade Center being that kind of structure, being a kind of skin structure, it was important that it have as well, a lot of load on it. It had to have weight on it, because if it were very light and you push on it, it would just tip right over. So it was important to have a lot of weight on it. And all of the interior columns that had been used in the past were a detriment. They were harmful to the design, because we didn't want those interior columns. We wanted that weight out on the outside, where it would do some good for this -- for the stalwartness of the building in resisting these giant loads from the wind.