The common thread that ran through most of the five day Petronio Alvarez Music of the Pacific festival that ended last weekend is acoustic marimba music from the Pacific coast. There, inhabitants of poor, isolated Afro-Colombian communities located amid mangroves and estuaries have clung to music styles their forefathers brought as slaves two or three centuries ago.

Among the 18,000 attendees who crammed Cali's Pascual Guerrero soccer stadium here for five days running were foreign documentary filmmakers, deejays, tour packagers and talent scouts. Many said they were seduced by the music's hypnotic quality and the frenzied audiences.

"It's very different, very mystical," said Pablo Ramirez, an organizer of the annual Vina del Mar music festival in Chile who was here to scout talent for his February event. "Maybe it's the fact that everyone in the stadium is dancing along with it, but the music is very penetrating. You can't help but move."

The festival's namesake, Petronio Alvarez, was a musician and composer from the port city of Buenaventura who died in 1966 after composing dozens of songs and poems about the everyday lives of poor Afro-Colombians. The inaugural festival was held in 1996 in an open air theater in Cali that seated a few hundred.

The success of the 15th annual festival - it was moved this year to a giant soccer stadium from the former venue, a 2,000-seat bullring - speaks to a long ignored musical genre getting its due. But the event's popularity also testified to the fact that African descendents comprising 15 to 20 percent of Colombia's population are claiming an increasing stake in a society that has long excluded them.

"Afro-Colombian culture is more visible not least because the people are more visible," said professor Juan Camilo Cardenas of University of the Andes in Bogota. "Displacement caused by decades of conflict has forced many more Colombian blacks from rural areas to the cities. And there is a push on for their equal rights with projects financed by U.S. aid."

The festival is also a competition, with bands vying for cash prizes and recognition that can lead to regional, U.S. or European tours.

Most of the 70 bands included one or more marimbas, 30-key, xylophone-like instruments. Others played guasas, a hollow tree branch with seeds inside that produce a rasping sound when shaken. Percussionists beat time on cununos, drums made with leather from the hides of tiny mangrove deer.

While Colombia's cumbia and vallenato music have worked their way into the "world music" mainstream, thanks partly to the popularity of pop singers Shakira and Carlos Vives, marimba is just now making inroads, said Will Sabatini, an BC-based deejay known as DJ Sabo. He attended the festival last year by happenstance, after being hired to work a show at a Cali nightclub.

He described the festival as a "life-changing event" and convinced several colleagues to attend this year.

"Marimba has a rootsy feel to it, a side of the African influence I had never heard before," Sabatini said. "With thousands of people in the stadium dancing along, it's a feeling you can't get anywhere else in the world. Among deejays who look to Latin music, it's really getting known.

But the Petronio Alvarez festival celebrates more than music. One end of the enormous soccer stadium was given over to a food court where dozens of Afro-Colombian communities sold handcrafts and offered up local dishes including pianguas (clams), cocadas (coconut and pineapple candies) and arrechon (a home-brewed aphrodisiac liquor).

The many facets of Afro-Colombian culture is what attracted Stephanie Scheiderman, owner of an Ann Arbor, Mich.-based tour packager called Tia Stephanie Tours. A marketer of "roots" cultural tours to Mexican-American and Afro-American travelers, Schneiderman said Colombia has only recently registered on the tourism industry's radar screen.

"African Americans want to learn about the diaspora of former slaves in other countries as well," Schneiderman said. "I came here because Colombia is an emerging tourism destination and I want to diversify my portfolio of offerings. I want to be on the ground floor."

On its final day Aug. 28, there were at least as many outside the stadium watching the festivities on giant video screens as the 18,000 spectators inside it.

Angel Beltran, the lead marimba player with the group called Socavon, and winner of the festival's top soloist prize, said the festival is helping poor Afro Colombian musicians seek better lives. The Colombian government recognizes the economic potential and is financing a marimba school that Beltran runs in his coastal town of Iscuande.

"The school is giving a skill to kids who otherwise would be on the streets and it exists because Petronio Alvarez gives value to what we do," Beltran said. "Every year, more people come to the festival and soon marimba will be as popular as cumbia, even more."