World Trade Center's Unfinished Legacy

The fire near the top of the World Trade Center’s north tower seared a new thought into those of us gaping at it from the streets of Lower Manhattan: the strong steel edifices surrounding us, sheathed in glass and stone and shimmering in the sunlight, were as mortal as we who stood in their shadow, and as the people who would have to somehow escape the biggest skyscraper of them all. Chatter rippled through Nassau Street. An airplane did that? Suddenly an explosion ripped to the left of the north tower, a wall of heat and flame. A terrifying stampede. What happened?