Flight 93 Memorial Gives Haunting Reminder of 9/11 Terror Attacks as It Opens in Shanksville, Pennsylvania

The Tower of Voices, a 93-foot-tall musical instrument holding 40 wind chimes, represents the 40 passengers and crew members of United Airlines Flight 93 who perished on 9/11. BioLinia and Paul Murdoch Architects. via National Park Service

Almost 17 years after the 9/11 attacks, a monument in Shanksville, Pennsylvania, was erected to commemorate the victims of the fourth hijacked plane, United Airlines Flight 93, which crashed into a field in rural Pennsylvania after its passengers and crew fought back against a group of terrorists.

The 93-foot-tall tower of wind chimes, named "The Tower of Voices," was unveiled on Sunday as the final feature of Flight 93's 2,200-acre memorial, reported Associated Press. The steel monument was built to remember the 40 heroes who perished after their plane, which was traveling from New Jersey to California, was hijacked the morning of September 11, 2001.

According to the National Park Foundation, which financed the project, the monument's purpose is "to create a set of 40 tones that can signify through consonance the serenity and nobility of the site, while also through dissonance, recalling the event that consecrated the site."

The monument is 93 feet tall, to coincide with Flight 93, and features dozens of windchimes, each representing one person aboard the flight and radiating its own unique sound.

"Together their voices will ring out into perpetuity, with this beautiful Somerset County, Pennsylvania wind," said Stephen Clark, the park's superintendent, reported USA Today.

On September 11, 2001, four hijackers took the cockpit almost an hour into the flight with the intent of striking the White House. As the airplane cruised above Pennsylvania, the passengers and crew heroically attempted to reclaim the plane and thwart the terrorists' mission.

"When they learned that, it galvanized them as a group," Clark said. "They said, 'We're not going back to any airport. This is a suicide mission.'"

After formulating a plan, the hostages stormed the cockpit where the hijackers were navigating the aircraft. A tussle broke out, which resulted in the plane crashing into a field below.

Paul Murdoch, the architect who created The Tower of Voices, said his vision was to celebrate their voices. "We wanted to do, I'll call it a living memorial in sound, because the last memories of many of the people on the plane were through their voices on phone calls," he said. "And we wanted to use the natural forces of the site to activate the chimes."

President Donald Trump is scheduled to arrive in Shanksville on Tuesday to attend the 17th- anniversary event. He will be joined by Pennsylvania Governor Tom Wolf and Interior Secretary Ryan Zinke.