Steel Fragment, Recovered

High-strength steel box columns, so called because of their rectangular shape and hollow center, outlined the footprints of the Twin Towers and provided structural support for the facade of each tower. This engineering and architectural innovation, which eliminated the need for traditional load-bearing masonry walls, had not previously been employed on such a large scale. Columns at the core of each building provided additional support for elevator shafts and utility conduits. Columns and beams at the perimeters of the North and South Towers formed a rigid frame of steel that ran the approximately 1,360-foot height of each building. At the Plaza level, columns were spaced 10 feet apart. They rose to the top of the fifth floor, where they branched into three smaller, more closely spaced columns. These architectural trees or tridents gave the towers their distinctive Gothic arch motif.