How the Twin Towers Were Built

The World Trade Center's Twin Towers used a steel-framed tube structure with concrete floors and glass curtain walls. Each tower had a central core (elevators, stairs, utilities) and a perimeter of closely spaced steel columns connected by beams, forming a rigid framework.

Key facts:

• North Tower completed 1973 (1,368 ft / 417 m); South Tower completed 1974 (1,362 ft / 415 m).
• 104 stories each; tallest buildings until Sears Tower (1974).
• Pre-cast concrete slabs were hoisted into place.
• Glass panels attached via aluminum cladding system.

The towers stood as icons of engineering until their destruction on 9/11/2001.