If people wanted to get from the ground to the top floor, they would need to jump from elevator to elevator, in the same way you might switch cars on a subway system. In addition to the support structure of the buildings, the WTC crew had to consider how people would actually get around the towers. In addition to utilizing an unconventional structural design, the Twin Towers were also an aesthetic departure from the older buildings in New York. Essentially, each tower functioned as three buildings stacked on top of one another. Essentially, each tower was a box within a box, joined by horizontal trusses on each floor. The crew lifted the steel sections into place using four large cranes (four per tower), mounted to long steel structures fitted inside the tube structure. The crew used excavating machinery to dig 3-foot (1-meter) wide trenches down to bedrock level. The grillage rested on a thick, concrete pad poured on the solid bedrock deep underground. In the spread footing design, each support column rested directly on a cast-iron plate, which sits on top of a grillage.

The grillage is basically a stack of horizontal steel beams, lined side by side in two or more layers. They repeated the process with 152 framework segments, each measuring 22 feet (6.7 m) across, to form a large box measuring four city blocks by two city blocks (about 500 x 1,000 feet, or 152 x 304 m). The construction process worked from the inside out. The process was pretty simple, at least conceptually. We have a rule," he continues. "Every car must be registered and driveable at a moment's notice at least 300 miles. Elevator systems have always been a difficult balancing act for skyscraper designers. It's tricky getting all the numbers to work out, and it functionally limits the size of the skyscraper. The only problem was that the soil inside the bathtub was the primary support means holding the walls in place - remove the dirt inside, and the weight of the dirt and water outside would push the walls inward. To keep the walls in place while they built up the foundation, the crew had to run underground tiebacks, cables extending from the perimeter walls to rock surrounding the bathtub.

Then they poured in concrete from the bottom of the trench while pumping the slurry out through the top. While the crew kept building upward, other workers started to flesh out the floors below, down to installing blinds and painting the walls. The WTC crew proposed a completely different system for the huge towers. Boosted by prominent appearances in several movies - such as the 1976 "King Kong" remake, Woody Allen's "Manhattan," and the "Superman" movies - the Twin Towers gained widespread recognition as a piece of New York. The excavation actually added 28 acres of prime New York real estate, forming what is now Battery Park City. In only a few years, the distinctive image of the Twin Towers was a staple on New York postcards, T-shirts and advertisements. The towers' fame was also fueled by several notable stunts. Business owners and residents were upset at being forced out of the construction site; citizens all over the city wondered why the Port Authority was sinking so much money into the project (estimated at more than $1 billion, the equivalent of about $6.8 billion today), apparently at the expense of public transportation facilities; environmentalists questioned some of the construction practices; and several prominent architectural critics said the towers were simply too big and ostentatious.

The Port Authority could build such tall towers because they had a huge plot of land with a large, open-area plaza. Instead, the Port Authority decided to use the unconventional "slurry trench method," previously employed mainly in subway construction. The buildings required a massive amount of steel - some 200,000 tons total - but the construction site only had room for a little bit at any one time. When they had dug down to the bedrock, they blasted away large pits for the towers' support structure and set about building the massive foundation structure for the buildings above. Massive skyscrapers need to rest on bedrock, the solid rock underneath the ground's soil, or they won't be able to stand up. This pyramid shape distributed the concentrated weight from the columns over a wide, solid surface. The tires should be squished down upon the 2" Composite Deck of the trailer and appear as if the ATV is carrying the weight of a rider. From a distance, felled trees going to the lumberyard resemble toothpicks when stacked onto the trailer. To finish each floor, the crew would pour concrete over the metal surface and top it off with tile.