The iconic twin towers of downtown Manhattan’s World Trade Center were a triumph of human imagination and will. Completed in 1973, the towers stood at 110 stories each, accommodating 50,000 workers and 200,000 daily visitors in 10 million square feet of space. They were the hub of the bustling Financial District, a top tourist attraction and a symbol of New York City’s–and America’s–steadfast devotion to progress and the future. On September 11, 2001, the World Trade Center became the target of a massive terrorist attack that took the lives of nearly 3,000 people. The disaster also radically altered the skyline of New York City, destroying the twin columns of glass and steel that over the years had come to embody the city itself.