If you ask me "Wichita Lineman" just might be the best song ever written. At the very least it's the first existential country song. As 1968 is currently being celebrated as the high-water mark of post-war cultural insurrection, it might seem perverse to lionise a middle-of-the-road ballad that harks back to a more innocent era, but Jimmy Webb's heartbreaking song was as evergreen then as it is now, and still seems to exist in a world of its own.

A dribble of bass, searing strings, tremolo guitar and one of the most plaintive vocals ever heard on record courtesy of Glen Campbell, Webb's paean to the American West describes the longing that a lonely telephone lineman feels for an absent lover who he imagines he can hear "singing in the wire" he's working on. Like all good love songs it's an SOS from the heart; there are even snatches of synthesizer-generated Morse Code heard after the lyric, "And the Wichita Lineman, is still on the line".

Webb, who had previously written "By The Time I Get To Phoenix" for Campbell, was asked by producer Al De Lory in October 1968 for a follow-up; and so he set to work, crafting another song based around a geographical reference. "Some time earlier," says Webb, "I had been driving around northern Oklahoma, an area that's real flat and remote – almost surreal in its boundless horizons and infinite distances. I'd seen a lineman up on a telephone pole, talking on the phone. It was such a curiosity to see a human being perched up there."

Putting himself up his pole, Webb spent two hours on his green baby grand in his apartment and wrote what he thought was three quarters of a song. "It wasn't finished," he says. "There was a whole section in the middle that I didn't have words for."

What Webb didn't know was that De Lory's uncle was a lineman in Kern County, California. "As soon as I heard that opening line," says De Lory, "I could visualise my uncle up a pole in the middle of nowhere. I loved the song right away." Overruling Webb's insistence that "Lineman" wasn't finished, De Lory laid synthesizer lines over the instrumental passage, one of the most evocative instrumental breaks ever recorded.

The following year Campbell and Webb were determined to make lightning strike thrice. Their next collaboration? "Galveston".

Dylan Jones is the editor of 'GQ'