An hour before the start of the race, J.P. Cappiello stood ready to go, immune to the morning chill but fighting the pre-run jitters.
"It's like before the curtain goes up, every possible bit of dread - and excitement," said Cappiello, a 41-year-old singer and bass player from Drexel Hill. "It's an end and a beginning all at once."
Beside him, likewise awaiting release from a color-coded corral, 59-year-old Joyce Sanyor battled her own nerves. "One foot in front of the other," the West Chester woman said.
They were two of the estimated 40,000 who took part in the 35th annual Blue Cross Broad Street Run on Sunday, traversing Philadelphia north to south via 10 miles of the city's signature boulevard. Last year, about 32,000 runners finished.
Cappiello wore a Star Wars shirt to mark the fan holiday - May the Fourth, as in "May the fourth be with you."
One man ran dressed as Spider-Man, a woman as the Tooth Fairy. One runner carried an American flag from end to end, helping to celebrate what has become one of the city's most popular and publicized events.
"You are . . . " Mayor Nutter began descriptively, addressing the runners moments before the 8:30 a.m. start, " . . . a lot of you!"
The blast of an air horn started the race, with runners released from pens in stages according to their expected pace.
It was at the starting line at Broad Street and Fisher Avenue in Olney that emotions turned acute. In the moments before the horn blares, runners say, they stand completely alone and completely surrounded, ready to embark on a solitary mission undertaken amid thousands of others doing the exact same thing.
"That anticipation is the worst - I'm literally shaking," said Janis Fratamico, 46, of Paoli, who on Sunday morning was poised to run with her friend Kelly DeCurtis, 43, of Malvern.
The start of the race is loud, the volume driven by the shouts of runners and fans, the movement of 40,000 bodies, and a public-address system that, of course, blares the theme from Rocky. Everyone in the race has something to prove, if only to him or herself.
"There's an energy in the air," said Trevor Payne, 43, a Radnor High School teacher who last week was preparing for his third Broad Street Run. "I feel the weight of all these people behind me, ready to follow after me."
It is, he said, as though the world shifts: You're in the middle of Broad Street, a space normally reserved for cars and buses. Sounds and sights magnify. As you move out, you can tell the difference in textures underfoot: stepping on a painted line feels different from landing on the asphalt beside it.
Everyone who is not running is cheering - not just the fans and families who come to watch, but people who have stepped out to grab their morning coffee or who are headed to church.
"There's this powerful civic energy," Payne said.
Allie Harcharek, 25, of Northern Liberties, a Wharton School marketing manager and blogger who competes in 10 to 15 races a year, has felt those emotions at the starting line.
"It's like a slow-building electricity in your body," she said last week as she prepared for her third Broad Street Run. "Standing there in that crowd, you can't help but feel the adrenaline."
Part of it is knowing that months of training are about to pay off. Part of it is the unstinting energy of the crowd and the racers, the joy of thousands of people focused on the same thing.
"It's this beautiful symbol of Philly itself," she said.
On Sunday, dawn brought a pink sun fighting its way through gray clouds, the morning turning cool and comfortable. The runners ranged from slow, weekend plodders to fast, elite athletes who crossed the finish line in an hour, while those at the back pushed onward.
As one, the throng bulged and narrowed depending on time and distance, people shedding extra shirts and sweat jackets as they went.
Moroccan Mourad Marofit claimed victory with an unofficial time of 47:06, and Bertukan Feyisa-Germane from Ethiopia won the women's race with a time of 55:26.
The 10-mile, point-to-point race goes almost from the top to the bottom of Philadelphia, ending about a quarter-mile inside the main gate of the Philadelphia Navy Yard.
Organizers warn that it's a race, not a walk, and runners must maintain at least a 15-minute-per mile pace or be directed to sidewalks so police can reopen Broad Street in a timely manner.
All along the way, music groups, church choirs, and cheerleaders shout and sing encouragement. On Sunday, the runners were greeted with balloons and cow bells.
"Mom! Mom!" a runner called out, wanting to be sure her mother saw her.
A rock band played oldies outside the Union League, bouncing Bob Seger's "Katmandu" across the intersection of Broad and Sansom.
As runners flashed by - or slowed to a walk - Caroline Credille, 29, of Philadelphia, held up a yellow sign: "At least you're not in The Hunger Games." The sign held by her friend Jennie Dougherty, 27, offered, "Worst parade ever."
They and Lindsey Wilson, 28, came to cheer a friend but wouldn't have missed the chance to be part of the race.
"So fun," Dougherty said.
"We've got to cheer our city on," Credille said.