It's been 25 years since 9/11, and I remember vividly, as so many do, the moment the second plane went into the South Tower, and how, in that moment, we all knew we were under attack. 

Many stories are being told, and many memories shared on the day. 

Here are just a few. 

Jules Naudet was following firefighters, including Battalion 1 Chief Joseph Pfeifer and firefighters from Engine 7, Ladder 1. He was doing a documentary as the crew looked into a mundane possible gas leak. That was when they caught the first plane hitting the North Tower. 

Warning for graphic language: 

You can hear the communications, with a fire official telling them to get everyone they could down there, as well as Pfeifer's assessment, even at that point, that the plane was "aiming" at the building. 

As he took charge, Pfeifer would later try to tell people trapped above that help was coming, as he heard people having to jump. 

After the South Tower came down, he ordered everyone out of the North Tower and helped get survivors out through the World Financial Center. He survived. His brother, Kevin, another firefighter, did not. 

There were so many amazing efforts to save people, including that of Battalion Chief Orio Palmer, who jury-rigged an elevator to make it to the 40th floor in the South Tower. He then climbed, with all his gear, up to the 78th floor, to the site of the strike.

He was still trying to help people when the South Tower collapsed. 

A PASS (Personal Alert Safety System) is a device that goes off when a firefighter is motionless for more than 30 seconds. The alarm helps you locate the first responder if he becomes trapped or is in need of aid. This was the sound of all the firefighters' PASS devices going off at the same time after the buildings came down. 

Members of Congress came together, Democrats and Republicans, on the steps to deliver a message of strength and spontaneously sang "God Bless America." 

What a message of unity. The sad thought I have is: Would they all do that today?