1 World Trade Center (North Tower) was the tallest building in the world from 1971 to 1973, until surpassed by the Sears Tower (now Willis Tower) in Chicago.
Many novel design, engineering and construction techniques were employed for 1 World Trade Center (north tower) and 2 World Trade Center (south tower) — which are collectively known as the Twin Towers. Innovations included a then state-of-the-art pressure equalized curtainwall system that dispersed wind load pressures upon the building structure rather than the external cladding, and an anchoring system that attached curtainwall units to the under side of the floor slab. Enclos provided design/build facade services for both the north and south towers, which included two million square feet of curtainwall.
The Twin Towers were destroyed in the September 11, 2001 terrorist attacks.