Monday will mark 16 years since the deadly 9/11 attacks.
To remember the estimated 3,000 people who died in New York, Virginia and Pennsylvania on September 11, 2001, people across the world participated in the 9/11 Heroes Run.
We asked some runners the where they were the morning of September 11, 2001.
"I was in California. I was an active duty marine," said Richard Delgado Jr., Race Director for the 9/11 Heroes Run in San Antonio.
"I was in first grade," said runner Sophie McDevitt.
"I had just gotten assigned to Ramstein Air Base," said runner Hector Nieves.
"I was in New York City," said runner Jarek Majdanik.
Runners in the 9/11 Heroes Run at Texas A&M University San Antonio ran to reflect and never forget the day our world changed forever.
"My mother actually put on the TV and it was on everything. CNN, CSPAN, Fox News. It was a rush of emotions for her. Just because I saw my mom pretty much in tears, I reciprocated that," said Nathaniel Nieves. "It was hard to understand at the moment what happened. I was only 7 years old at that time."
"I remember over the PA system they said planes flew into towers," said McDevitt. "I just remember it was a solemn day. Every year when it gets around that time, I remember those feelings I had...I come from a military family so this really hit home for me."
Many of Sunday's runners were on active duty during 9/11.
"We shut down the base and we were going through our recall roster to make sure all the marines in our unit came back," said Delgado.
"We had seen the smoke from the first aircraft in the report," said Nieves. "There was about 20 of us in a room, Air Force people, watching the screen and we saw the second aircraft hit the other tower."
Majdanik worked in Manhattan at the time.
"When the second airplane hit, which I actually saw from the street of my house, I knew something bad had happened," he said. "It wasn't just an accident. We knew somebody had to be behind it."
Two weeks later, Majdanik joined the military.
"I joined the US Army," he said.
The race director tells us the hero title isn't just for law enforcement and military, it's for the average, ordinary citizens who also risked their lives that September day.
"We saw it in Houston and the Gulf Coast with Hurricane Harvey," said Delgado. "So 9/11, we just don't want to forget the meaning and how it truly changed the landscape of the United States."
Among the runners were nine members of the Flags 4 Fallen organization.
Each volunteer carried a full-size U.S. flag in honor of the nine fallen SAPD officers who died in the last ten years.
Jacy Rugaber, a Flags 4 Fallen volunteer and military service member, ran in honor of Officer Robert Davis. Davis was struck and killed by a fellow police officer's patrol car as he cleared flares from a previous wreck in November 2008.
"It gives you more of a sense of purpose when you're running," said Rugaber." You're not doing it for yourself. You're doing it for something that's much bigger than you. I think that's the motivating factor, knowing that it's not for you. It's for the person who can't run anymore," said Rugaber.
Each volunteer handed the flags to San Antonio police officers who will gift the stars and stripes to families of the fallen.