The late Minoru Yamasaki, chief architect on the WTC project, had this to say about the Twin Towers, on their completion in 1973:

"I feel this way about it: World trade means world peace and, consequently, the World Trade Center buildings in New York ... had a bigger purpose than just to provide room for tenants. The World Trade Center is a living symbol of man's dedication to world peace. Beyond the compelling need to make this a monument to world peace, the World Trade Center should, because of its importance, become a representation of man's belief in humanity, his need for individual dignity, his beliefs in the cooperation of men, and through cooperation, his ability to find greatness."

A great little article about the towers is available here.