LOS ANGELES — It was 1906 when William Seymour, the son of slaves, traveled to a small church to preach that speaking in tongues was the ultimate path to salvation. The congregation rejected his message and promptly kicked him out.

But that wasn't the end of the story.

Committed to his belief, Seymour started his own prayer group — first at a friend's house and then at an abandoned church in northeast Los Angeles. Within weeks, people of all races were streaming to the City of Angels to see the services where worshippers fell to the ground and uttered strange, unintelligible sounds.

The boisterous, three-year revival that followed made international headlines and is widely credited as the birth of modern-day Pentecostalism. The movement, once relegated to the theological fringe, now claims up to 600 million followers worldwide and remains one of the fastest-growing sectors of Christianity, according to Vinson Synan, dean of Regent University's School of Divinity and an ordained minister of the Pentecostal Holiness Church.

Starting this weekend, up to 60,000 followers will descend on Los Angeles to mark the movement's 100th birthday, a celebration that begins with a visit to the street corner where the revival church once stood. The Azusa Street location, now in the heart of Little Tokyo, bears a commemorative plaque.

"We see the centennial as a homecoming for the movement, a wonderful memory of what God did 100 years ago," said the Rev. Billy Wilson, executive director of the Center for Spiritual Renewal, the celebration's sponsor. "We want to show the world that Pentecostals are about more than just feeling good and speaking in tongues."

Pentecostals believe in a personalized commitment to Christ and a second experience known as "baptism in the Holy Spirit." That baptism is most commonly accompanied by speaking in tongues, though other "gifts" from the Holy Spirit can include faith healing, the casting out of demons and modern-day prophecies. Followers base the practice on Acts 2:1-4, in which Jesus' apostles were "filled with the Holy Spirit and began to speak in other tongues, as the Spirit gave them utterance."

Mainline Christians had rejected speaking in tongues for more than a thousand years, believing that the Holy Spirit's gift stopped with the apostles. But when Seymour came to Los Angeles in 1906, conditions were ripe for the long-forgotten message.

The rough-edged town of 240,000 residents had doubled its population in just six years, and the city sprouted so many new churches that modern-day experts have called it an "American Jerusalem."

Hundreds of Christians were so concerned about the freewheeling mentality of the rapidly growing city that they had broken away from mainstream denominations to pray for a massive spiritual revival.

Those concerns reached a fever pitch on April 18 — just five weeks after Seymour's arrival — when San Francisco was rocked by a massive earthquake. Many saw the quake as a sign of the apocalypse.

The same day as the disaster, a major Los Angeles newspaper published a front-page story about Seymour's strange prayer meetings — all-night services so rowdy that two policemen were posted full time at the church to keep order. The story bore the headline "Weird Babel of Tongues: New Sect of Fanatics is Breaking Loose."

Soon, all eight major newspapers were covering the revival, as were religious newspapers called "holiness circulars" that were passed among evangelical churches nationwide. Word spread across the nation — and then the world — about the massive revival under way in Los Angeles.

One of the revival's most notable characteristics, experts say, was that blacks and whites worshipped under the same roof and shared pastoral duties.

"At its height, it drew people from all classes, wealthy and poor, Hispanics, blacks, Jews — you name it, everybody came," said Synan. "Whole churches collapsed and joined it. There was a force there, it was almost supernatural. People said they could feel it in the air from about three blocks away."

Within eight months, nearly 20 missionaries from the revival struck out for Africa, India and China to start Pentecostal churches, said Cecil M. Robeck Jr., professor of church history and ecumenics at Fuller Theological Seminary in Pasadena.

Revival attendees also established Pentecostal churches across the South and the Midwest, including the Pentecostal Holiness Church, the Church of God in Cleveland, Tenn., and the Church of God in Christ in Memphis.

Pentecostalism's influence can also be felt in other evangelical churches, particularly in the music and worship style of megachurches, Synan said.

"I can go into almost any Baptist and Methodist church and feel like I'm in a Pentecostal church," he said. "They sing the same songs, the same choruses, they lift their hands."

Today's Pentecostals are less likely to speak in tongues, however, perhaps in part because the practice caused them to be shunned by some mainline denominations. Experts estimate that only 40 percent of Pentecostals speak in tongues today, and even fewer do so overseas, where the movement is growing the fastest, Robeck said. "That's a real pastoral issue these days," he said. "We still do argue that every Pentecostal should have that ability but a lot of folk are not following through with it."

Those attending the centennial celebration, including a who's who of Pentecostal preachers, hope to address those concerns and plan their ministry for the next 100 years.

"Pentecostals are no longer as much on the wrong side of the tracks and are again in the mainstream of evangelical life in America," Wilson said. "We want to evaluate what has happened. Have we gone the right direction with what God originally did?"