TEMPE, Ariz. (AP) -- Every April, 28,000 runners descend upon the Arizona State University campus to cover the 4.2 miles of Pat's Run.
The run started in 2004 as a way to honor Pat Tillman, the football player killed by friendly fire in Afghanistan after leaving a lucrative NFL career.
Pat's Run has blossomed into much more since that inaugural run in San Jose, California, becoming a way to honor a person considered to be a hero by many and to support the foundation that bears his name.
Pat's Run has since branched out beyond the desert as people across the country joined in shadow runs in conjunction with the main event in Arizona.
This weekend, more than 3,200 people in 32 cities will run 4.2 miles in what are now called honor runs to recognize Tillman's life and the way he lived it while raising money for the Pat Tillman Foundation.
''It's just a meaningful experience for people,'' said Trish Thiele-Keating, program manager of the Arizona State Alumni Association. ''They feel a connection to Pat and want to show their support, even if they can't run in Arizona.''
The first Pat's Run was a way for family and friends to honor a man who lived a push-it-to-the-limit life, someone who walked away from a multimillion-dollar NFL contract to serve his country in the wake of the 9/11 terrorist attacks.
The run shifted to the desert a year later with 5,000 runners and grew as people came to know Tillman's story, his approach to life and untimely death, touching many who had nothing do with Arizona State, the Arizona Cardinals or the military.
In 2009, the Pat Tillman Foundation decided to branch out, offering shadow runs in eight different cities for its Tillman Scholars and anyone who wanted to be a part of the run and couldn't make it to Arizona.
A few hundred runners participated in the first shadow runs and they quickly expanded as more people wanted to be a part of Pat's Run without travelling to Arizona. Thiele-Keating helps coordinate the runs, but the on-the-ground operation is all done by volunteers.
The runs tend to be in iconic places: Around historical monuments in Washington, D.C., along the beach in Los Angeles, past the piers along the Hudson River in New York, past the Golden Gate Bridge in San Francisco, along the Charles River in Boston.
New York has the largest honor run with about 700 runners, while cities like Atlanta, Washington and Charleston, South Carolina, have 300 or more.
''It's really just in honor of Pat's legacy,'' said George Sondecker, a former Tillman Scholar who now helps build rockets at SpaceX and will participate in the Los Angeles honor run. ''He's a national hero as far as I'm concerned. It's a wonderful way to honor his life, the sacrifice he made. He's certainly an exemplar in character and honor signing up to serve our country when our country needs us. It's wonderful for people all around the country to come out on that day, the day of Pat's Run, to remember him. It's a pretty symbolic gesture.''
Pat's Run and the honor runs that coincide with it have become the major fundraiser for the Pat Tillman Foundation, which helps bridge the financial gaps in the GI Bill by providing scholarships to veterans or their family members transitioning to their academic lives.
The foundation has raised more than $14 million in academic support and much of that has gone to the Tillman Scholars, top-tier students who often impact the world well beyond their academic careers.
Tillman Scholars are spread across the country and the world, so the honor runs give them a chance to not only stay connected and support the Tillman Foundation, but to thank some of the people who helped make their educations possible.
''It's a really good opportunity for the Tillman Scholars to thank people who may not be able to make it to Arizona, but still support the Tillman Foundation,'' said Michelle Neveu, an Air Force veteran who just completed her nurse practitioner master's degree. ''My hope is that they can meet people they impact directly just by running this race.''
Pat's Run attracts people of all shapes, sizes and abilities. While the high-level athletes race to the finish line, many of the runners behind them labor through the course; veterans with prosthetic limbs, overweight runners pushing themselves to keep going, people with severe disabilities unwilling to quit because Tillman never did.
A year ago, the runs in the Northeast were darkened by storms. Wet and cold, the runners pushed each other toward the finish line, their shared discomfort becoming a rallying point, much like soldiers uniting when faced with difficult circumstances.
''It's almost made the event that much better,'' said Nick White, a medical student at Columbia who will run the New York City honor run for the second straight year this weekend. ''It was a little bit miserable, but the shared misery is something that is familiar to people who have been in the military. There's a lot of comradery.''