WASHINGTON - With the official opening of the Pentagon Memorial a week away, the chairman of the Joint Chiefs of Staff reflected on the events of nearly seven years ago that inspired the memorial's creation.

Navy Adm. Mike Mullen said his life as an American and as a servicemember changed forever on Sept. 11, 2001. The surprise attack not only took the lives of more than 3,000 people that day, but also revealed the capabilities and threat of terrorism and set the stage for current military operations in the Middle East.

"It was a brand new world. ... [The 9/11 attacks] were unexpected. It was a surprise, and it was also recognition we had an extremely serious threat, a terrorist threat, an extremist threat," he said during an interview at the memorial with the Pentagon Channel.

That day at the Pentagon, 184 people lost their lives when the hijacked American Airlines Flight 77 crashed into the building. The memorial in their honor is just outside the crash site, and each victim is represented with his or her name inscribed on one of 184 sculptural elements illuminated by lighted reflection pools below.

"It's an incredibly important memorial to remember those who've sacrificed," Mullen said. "[The memorial] is a representation of so many special people, so many special thoughts, but most importantly, it's a representation of those who were lost and their families who sacrificed so much."

Remembering those who lost their lives on Sept. 11 and since then in Iraq and Afghanistan is one of the biggest concerns expressed by grieving family members. They fear that one day future generations will forget their loved ones' sacrifice, the admiral said.

"For those who are young, I would tell them how special [the memorial] is and how special those people are who we lost," he said, "and what it means to be an American and sacrifice, which is at the heart of who were as Americans since we've been a country."

The 9/11 attacks led to immediate action against al-Qaida in Afghanistan, and in March 2003 U.S. military offensives were launched in Iraq. Today, more than 4,500 U.S. military members have been killed fighting terrorism in the two countries and are very much connected to the 3,000 people killed on 9/11, he said.

"[The memorial] also serves as a very visible reminder of the renewal that took place that day," Mullen said, "the resilience that we have as a country and a people and the commitment we have to defeat this threat and to never let it happen again."

The memorial is scheduled to open to the public at 7 p.m. on the attack's seventh anniversary. More than 5,000 people are expected to attend, Pentagon officials said.