A few weeks after the song’s release, 24-year-old Johnny Cash performed “I Walk the Line” on The Grand Ole Opry, with Ben A. Green of the Nashville Banner in the audience. “The haunting words of ‘I Walk the Line’ began to swell through the building,” Green wrote (in a review later featured in The Man Called Cash by Steve Turner), “and a veritable tornado of applause rolled back. The boy had struck home, where the heart is, with his song that is Number 2 [on the Billboard country chart] in the nation today. As his words filtered into the farthermost corners, many in the crowd were on their feet, cheering and clapping.”

With its gradual boom-chicka rhythm, hummed verses, and words of vigilance against moral lapses, “I Walk the Line” (released on May 1, 1956) stood out among the fast and frisky songs on the radio. “It was different than anything else you had ever heard,” Bob Dylan once told Rolling Stone. “A voice from the middle of the Earth.”

Cash wrote the lyrics while touring in Texas. It was a promise to stay faithful to his first wife, Vivian, amid the temptations of the road, with the underlying spiritual theme that’s weaved through much of Cash’s work.

As for the melody, it’s older and came about in a more ghostly way. In 1951, Cash was a U.S. airman, stationed at a base in Landsberg, Germany. He and a few other servicemen played in a country and western band called the Landsberg Barbarians. In Cash: The Autobiography, the artist said that he purchased a reel-to-reel recorder “with savings from the eighty-five dollars a month Uncle Sam paid me to fight the Cold War.” Cash further recounts:

I was on the eleven-to-seven shift in the radio intercept room one night, listening in on the Russians, and when I got back to the barracks in the morning I discovered that someone had been messing with my tape machine. I put on a Barbarians tape to test it, and out came the strangest sound, a haunting drone full of weird chord changes. To me it seemed like some sort of spooky church music, and at the end there was what sounded like somebody saying "Father." I played it a million times, trying to figure it out, and even asked some Catholics in my unit if they recognized it from one of their services (they didn't), but finally I solved the puzzle: the tape had gotten turned around somehow, and I was hearing Barbarian guitar chords played backward. The drone and those weird chord changes stayed with me and surfaced in the melody of "I Walk the Line."

The melody was down, and Cash had the unique chord progressions when he first began recording for Sun Records in 1955. His original was slower, but, according to Johnny Cash: The Life by Robert Hilburn, Sun Records owner Sam Philips coaxed him into recording an up-tempo version and released it without telling Cash. Cash was surprised to hear that version on the radio while on tour and phoned Philips.

“Give me just two weeks,” Philips replied. “If it doesn’t do what I think it’s going to do, I promise you right here, I’ll pull the record and we’ll release the slow ballad.”

He never released the slow ballad.