One World Trade Center was ready for its first tenants in late 1970, though the upper stories were not completed until 1972.

Windows of the World Restaurant (the world's highest) occupied the 107th floor.

World's tallest building from 1972 - 1974; surpassed by the Willis Tower in Chicago.

Replaced the Empire State Building as the city's and the world's tallest building.

The building was destroyed in the terrorist attacks of September 11th 2001, when a Boeing 767 was flown into the building at the 85th floor at roughly 9:00 am. The building collapsed at 10:28 am.

Faced with the difficulties of building to unprecedented heights, the engineers employed an innovative structural model: a rigid "hollow tube" of closely spaced steel columns with floor trusses extending across to a central core.

The columns, finished with a silver-colored aluminum alloy, were 18 3/4" wide and set only 22" apart, making the towers appear from afar to have no windows at all.

Also unique to the engineering design were its core and elevator system.

Worried that the intense air pressure created by the buildings' high speed elevators might buckle conventional shafts, engineers designed a solution using a drywall system fixed to the reinforced steel core.

The twin towers were the first super-tall buildings designed without any masonry.

On 7th August 1974, French high wire artist Philippe Petit made an illegal tightrope walk back and forth between One and Two World Trade Center towers that lasted almost an hour.