The problem wasn’t building to the sky, it was digging into the earth. Before any steel went up, men had to build a fortress down–The site was landfill, soft and wet from the Hudson.

To dig the foundation, they had to hold back the river.

The solution was a “bathtub,” a massive concrete slurry wall driven eighty feet down to bedrock.

They dug a trench, filled it with a thick clay slurry to stop the walls from collapsing, then pumped in concrete – This wall encircled the site, a dam to keep Manhattan dry.

Inside this box, they also had to work around the PATH train tubes, suspending them in midair while they dug out the earth below – It was a brutal, delicate job.

Only then could the towers rise – The design was new, a hollow tube of closely spaced steel columns on the outside carried the weight and fought the wind – This left the floors open, with no need for interior columns.

Prefabricated floor sections, steel trusses topped with concrete, were hoisted and locked into place. In the center, a steel core housed the elevators and stairs.

To build higher, they used self-raising “kangaroo” cranes from Australia – These machines used hydraulics to jump up the building as it grew, floor by floor–It was a race, a new way to build a new kind of giant.