September 11th: How and Why the Twin Towers of the World Trade Center Fell

The story of September 11th begins not with the events of that terrible day, but with the revolutionary design concepts that made the World Trade Center possible. When architect Minoru Yamasaki and structural engineer Leslie Robertson began planning the towers in the 1960s, they faced an unprecedented challenge: creating the world's tallest buildings on a site constrained by Manhattan's dense urban environment and complex underground infrastructure.

Their solution was revolutionary. Rather than using the traditional approach of massive internal columns and thick exterior walls, they developed what became known as a "tube-in-tube" design. The exterior walls would bear most of the building's weight, with closely spaced steel columns creating a rigid outer shell. This design allowed for vast, column-free interior spaces while using significantly less steel than conventional construction methods. The core of each building contained elevators, stairwells, and essential services, surrounded by a grid of steel columns that provided additional structural support.