When they were completed in 1973, the two towers of the World Trade Center were the world's tallest buildings.
They were designed by Minoru Yamasaki & Partners and Emery Roth & Sons, with Worthington Skilling Helle & Jackson as structural engineer.

The towers had an unusual feature: they were supported by load-bearing external walls and internal cores. There were no columns intersecting the office floors, giving a highly efficient floorplate (see below).

The external walls consisted of thick load-bearing columns in aluminium-clad steel, which alternated with narrow windows. These acted as giant vierendeel trusses but gave the building an oppressive cage-like appearance.