At 7:46 a.m., city leaders observed a moment of silence.
It was 15 years to the minute that the first plane crashed into the North Tower of the World Trade Center, changing the U.S. and how it looks at terror forever.
Mayor Emanuel reflected on that day and on those who served.
"In a selfless act, while other people were running down a flight of stairs they (firefighters) were running up a flight of stairs to serve their fellow citizens and to save them. And our Chicago firefighters answered that call also. It wasn't our city, but it was our country. It wasn't their fellow residents, but it was their fellow citizens," Emanuel said.
Flags will fly at half staff throughout city police and fire stations for 72 hours to honor the victims.