Although Sidney Baptista was born and raised in Dorchester, the Boston Marathon might as well have been a world away when he was a kid.

“Growing up in Boston, everything you see about Boston on the media was never about the parts that I lived in. So it was also foreign to me," he said of the marathon, which will see its 125th running on Monday. "So I would just be like, ‘Oh…we’ve got to go into the city to experience all of this stuff.’ And the Boston Marathon was one of those things. It was just an event that happened that I watched on TV and had the weekend off.”

While named after the city, most of the Boston Marathon isn’t actually run in Boston proper, but through its affluent suburbs. When the course finally does enter city limits, anything south of Copley Square might as well not exist.

Whether intentional or not, it’s an oversight that leaves out places like Dorchester, Roxbury and Mattapan in favor of Wellesley, Newton and Hopkinton. For Baptista, this oversight is another example of how one side of the city gets left out of the popular narrative.

“Like when you watch movies, it’s about majority white areas of Boston. They’re not really (showing) the other neighborhoods of Boston," he said. "It potentially shaped the perspective of what people have of Boston."

On Saturday, Baptista and the PIONEERS Run Crew, a running club based in Dorchester, are aiming to upend that narrative by hosting 26.TRUE, a marathon that starts and ends in Malcolm X Park in Roxbury. The route goes through parts of the city that most Marathon Mondays ignore.

The idea for an alternative marathon has been brewing for a long time. Barak Soreff, who charted the course of the new race, says members of PIONEERS use an app that helps map hot spots for runners.

Data from the app gives a stark picture of where runners go and where they don’t. Some of the coldest spots in the city are Dorchester, Roxbury and Hyde Park.

“And so the fact that these areas aren’t represented, when Dorchester’s the biggest neighborhood in the city, and we’re just seeing that people aren’t running here, it just kind of got us thinking," he said.

A map of Boston showing the downtown area, and a 26.2-mile marathon route in purple.

When the 2020 Boston Marathon got pushed to a virtual-only format because of COVID-19, it gave PIONEERS runners who had qualified a chance to run their own course through the city, a soft launch of what was to come. This year, when the Boston Athletic Association announced a smaller in-person field with opportunities for virtual participants, light bulbs started to go off.

“And we like, took a step back, and were like, ‘Wow, there’s like 25, 30 people that are like all of a sudden throwing their hat in the ring to do this virtual event," Soreff said. "And we’re like, ‘Well, if this many people are doing it, why don’t we create our own event and make it something special?’”

At a weekly meeting of PIONEERS the Wednesday before the Oct. 11 marathon, runners do one- and three-mile treks through Dorchester before picking up their bibs and shirts for the 26.TRUE run. It’s clear from the cheers and the camaraderie between the runners, many of whom are Black and brown, that this gathering is more than just a workout.

For some, like Bruce Martin, who has run four of the six world marathon majors, including Boston twice, 26.TRUE is a chance to bring something new to Boston running.

“People who look like us, they’re going to see us. Everybody might not see us, but those who are out, they see the bibs — they’re gonna cheer," he said. "And they’re gonna egg us on and keep us motivated to keep going. And I think that it’s gonna bring some more acceptance to runners of color running.”

26.TRUE will be Lizet Medina’s first marathon. She’s especially excited about the chance to get her first marathon medal while also highlighting parts of Boston that are often overlooked — and maybe set an example for future generations.

“I mean honestly, one of my friends, she’s gonna bring her kids, ‘cause she’s like, ‘I just want to see my kids seeing a group of people of color running in Boston like that, like something major like that," she said.

This weekend is going to be a busy one for Baptista and his crew. Along with 26.TRUE, they're hosting multiple events to commemorate the Boston Marathon and they'll be included in the BAA's opening ceremonies.

It's a partnership that goes beyond the finish line: The BAA is working with PIONEERS and other running groups to start theBoston Running Collaborative, an effort to increase access to the sport. Baptista admits that at first, he was skeptical of working with the BAA, but he's been blown away by what they've done since.

"I think a lot of companies, brands and organizations try to sometimes do everything," he said. "But what they've acknowledged and realized is that there are communities and organizations like PIONEERS Run Crew that are doing the work, so you don't have to come and do the work, just support the communities that are doing it. And with that, I've seen they're bringing a lot of different voices to the table that they're receptive to."

Saturday’s alternative marathon will offer more than just a new way to run Boston for Baptista, whose message wasn’t always well received when he started speaking out. And while runners are notoriously competitive, the race, and what it represents, may be its own sort of prize for the trailblazers forging a path for runners looking for a place beyond the big finish line in Copley Square.

“I remember doing an event for my birthday and I remember a local running leader describing it as like, ‘Go join Sid’s ghetto run,'" he recalled. "But from that, to now this, where we’re like (getting) people excited, running in the neighborhoods that no one’s ever wanted to run in before or have acknowledged — for me, it’s a celebration. It’s a culmination of the hard work, dedication that this group of volunteers that is PIONEERS Run Crew has put together.”