He was taken by the way the profession runs in families. Former driver Donald "Manboy" Savoy, 80, is still a daily presence at the North Fremont stable. His sons Donald Savoy Jr. and "Frog" Savoy, grandson James "Fruit" Chase, and great-grandson Ahmad Chase all still help run the place.
Likewise, James "Pookie" Rich, 43, has been an a-rab for 30 years, and his daughter Weedy Rich, 22, has taken up the tradition, becoming one of the few female a-rabs. "I'm horse-crazy just like my father," she says.
Warren noticed something else of importance. Threatened as they are, a-rabs can get produce into "food deserts," places where low-income residents have little access to supermarkets that sell fresh fare.
"They're not a relic. They're relevant," Warren says.
He became so well versed in the culture he was nominated a vice-president of the Arabber Preservation Society. In that role he began hatching his plan for creating a site that will be "a stop on the city's cultural map."
He decided to try "reverse development" — instead of seeking financial investment, then adding art on top of a completed product, he'd "come in with art first, making a cultural investment that would inspire financial investment."
He engaged the services of Gaia, a New York- and Baltimore-based street artist who has created murals in places as far-flung as England, Argentina and Indonesia.
"At first I didn't see how a-rabbers and street art cohered, but when I realized it was about connecting disparate cultures, I got involved," the artist said in the stable on Tuesday.
He contributed several murals, including one that depicts the four generations of Savoy's family, a work that attracted visitors and photographers as he went.
Several other well-known street artists added pieces on and around the site, depicting horses at work, green cropland and other individuals who have been "mainstays" at the stable.
In May, the group set up a "kickstarter" social-media fundraising effort that drew on their professional and personal contacts. It raised nearly $6,000 overnight, about a third more than they expected.
If Sunday's event goes well — and Warren expects everyone from Sandtown neighbors and a-rabs to City Council members — it could make the project more attractive to the nonprofit and government foundations that invest in urban revitalization projects.
The event will feature music, pony and carriage rides for children, two marching bands, a moon bounce and local cuisine. "It will be half pop-up gallery, half West Baltimore barbecue," Warren says.
Long-term goals, he adds, include getting the stable's roof repaired, incorporating three adjoining green spaces and rehabilitating the stable's interior to allow for art and video installations and events for school children. Total cost: an estimated $60,000.
On Tuesday, Gaia and two colleagues, the artists Nanook and Sorta, worked to complete murals in time for Sunday. Workers loaded wagons with watermelons for the afternoon's runs. And the "Fruit Man" took a break from watering a pony with a hose.
He's been a-rabbing since grade school, he says, and he has no plans to quit soon. Nor do his colleagues. It's not just their livelihoods at stake. It's a way of life.
"We're a group of people that won't give up until the bitter end," he says. "Why let something die that works?"