Sunday marked 15 years since terrorists hijacked four commercial planes and crashed them into the Twin Towers of the World Trade Center, the Pentagon and a field in Pennsylvania.

The attacks began at 8:46 a.m. Eastern time when American Airlines Flight 11 crashed into the north tower of the World Trade Center. Just 17 minutes later, at 9:03, America watched as United Airlines Flight 175 crashed into the south tower. America then realized it was under attack.

At 9:37, American Airlines Flight 77 crashed into the Pentagon in Washington D.C. About half an hour later, at 10:03, United Airlines Flight 93 crashed into a field in Shanksville, Pennsylvania, after passengers attempted to take control of the plane after hearing about the other attacks.

The Twin Towers in New York collapsed by 10:30 a.m., and by days’ end, President George W. Bush declared terrorists had attacked America.

As it does every year, America paid tribute on the 15^th anniversary of the attacks.

In Wichita, firefighters from around Kansas honored the 343 firefighters killed on 9/11. KWCH Channel 12 reported the firefighters climbed 110 flights of stairs at the Epic Center in downtown Wichita wearing their full gear on Saturday. That number represented the number of floors in the towers.

Firefighters participating in the stair climb were assigned a name badge and picture of one of the firefighters killed on 9/11. Money raised at the event will go to the Fire Department of the city of New York’s Fire Family Transport Foundation.

President Barack Obama said Sunday the nation will never forget the lives of those killed on 9/11.

Obama, while attending a Pentagon memorial service, said he is inspired by the resilience of the victims’ families, the Associated Press reported. He quoted biblical scripture: “Let not steadfast love and faithfulness forsake you. Bind them around your neck. Write them on the table of your heart.”

At Ground Zero, following a moment of silence at the time when the first plane hit the north tower, families of the victims gathered and read the names of those killed in the Twin Towers and surrounding area.

In Pennsylvania where Flight 93 crashed, the 40 passengers and crew members were honored with a reading of names and tolling of bells. The AP reported hundreds have taken part in the annual service at the Flight 93 National Memorial in Shanksville.

Obama praised the country’s diversity and urged Americans not to let their enemies divide them. He called the day difficult but added it is one “that reveals the love and faithfulness in your hearts and in the heart of our nation.”