The driving forces behind the construction of the World Trade Center are devastated by its destruction.

Builder John Tishman, 74, whose company Tishman Realty & Construction erected the Twin Towers slab by slab in the late ’60s and early ’70s, is so distraught, he is barely speaking.

He and his son, Dan, along with other company officials, gathered in a small office at the company’s headquarters at 666 Fifth Ave. to watch on television as the towers pancaked into mounds of debris.

Tishman spokesman Richard Kielar said the group sat in stunned silence, unable to take their eyes off the horror on the TV screen.

“John keeps a lot of feelings to himself,” Kielar said, “but he is obviously upset.”

Banker and developer David Rockefeller, whose idea to spur downtown development sparked the towers’ construction, watched from his Rockefeller Center offices as they collapsed.

“It was one of the most effective, as well as frightening, evil acts this country has ever experienced,” he told The Post. “It was obviously well planned and executed.”

Rockefeller said that, despite the security measures implemented after the 1993 WTC bombing, he doesn’t see how anyone could have guarded against “people willing to give their lives to bring about the suicide bombing. It was a manned missile.”

Of the buildings his vision helped create, the 86-year-old Rockefeller said, “It never occurred to me it could arouse this kind of evil attack. I don’t think anyone ever imagined it. It was alarming.

“The personal tragedy is enormous.”

As head of the Downtown Lower Manhattan Association in the 1960s, Rockefeller lobbied his brother, then-Gov. Nelson Rockefeller, to promote the construction of the complex.

Because it was conceived as a project to promote international trade – which largely came through the New Jersey ports – they rounded up the support of the governor of New Jersey, who insisted it should be located on the West Side of Manhattan, facing Jersey, rather than the originally proposed East Side location.

The bistate Port Authority was put in charge of development.

Guy Tozzoli, who headed up overall development for the WTC at the Port Authority, is now president of the World Trade Centers Association, an organization of more than 300 centers in almost 100 countries. Its offices on the 77th floor of the north tower were destroyed.

On the day of the attack, he was late to a meeting there because of an auto accident at the Lincoln Tunnel. By the time he drove to the plaza at the Holland Tunnel, the Twin Towers were in flames.

“I saw the north tower burning,” Tozzoli said, and watched as the second plane came in full throttle. “I said, My God the people above it have very little chance of getting out.”

When designing the tower, architects and engineers used a computer model to simulate the impact of a jetliner crashing into the towers.

They developed an imaginary scenario in which a fog-bound Boeing 707, flying at 200 miles an hour, was trying to land, couldn’t find the runway and hit the tower.

“The computer told us . . . it would blow up seven floors on one side but the rest of the building would be fine,” he recalled.

“Now they are bigger planes, and the terrible guys that did this knew what they were doing. That’s why the towers came down.”