It's late on a sultry May night in Clarksdale, Mississippi and, in the Hambone Gallery, before a small audience, three men are playing the blues. One is gently chording an acoustic guitar, the second plays in a traditional blues style, fingers walking up and down the neck like a lifer patrolling a tiny cell; the third is a virtuoso, playing high up on the neck, firing off showy trills and glissandi that leave us watchers open-mouthed. There's no stage. The floor is bare. The musicians sit on wooden chairs.
Here, in the poorest region of the poorest state in the Union, the blues were born like this. They started life with individual black musicians wrenching wails and cries from bashed-up instruments in front of small, rapturous crowds. The guitar virtuoso, Sean Appel, bearded yet baby-faced (he could be Seasick Steve's rubicund grandson) puts his Gibson in its case and chats to the audience about his town. "This is a magical place. You can meet people here in their 80s and 90s who knew John Lee Hooker! I'm telling you. Honeyboy Edwards, he's 96 years old, he played with Robert Johnson, and you can see him in the street!"
Clarksdale is on "Blues Alley", a 196-mile section of Highway 61 that runs from Memphis to Vicksburg – and runs on and on, in both directions, down to New Orleans and up to Minnesota. It's the road that took black Mississippi fieldworkers away from slavery and poverty, north and south into major cities where they could improve their lives – and the road that spread the blues across America, as the migrating masses carried the music with them.
The Highway was celebrated by Bob Dylan on his sixth album, Highway 61 Revisited, full of blues songs of travel, threat and desolation. The road was important to him. It runs through Duluth, Minnesota, where he was born, and Hibbing, Minnesota, 75 miles away, where he grew up. Its symbolism as a road to freedom is clear. In his autobiography, Chronicles, he explains: "[When young] I was into the rural blues as well; it was a counterpart of myself. Highway 61, the main thoroughfare of the country blues, begins about where I came from... Duluth to be exact. I always felt like I'd started on it, always had been on it and could go anywhere from it, even down into the deep Delta country. The Mississippi River, the bloodstream of the blues, also starts up from my neck of the woods. I was never too far away from any of it. It was my place in the universe."
To mark Dylan's 70th birthday, on 24 May, I decided to travel down it, to see what can be found there, a century after the early bluesmen were born. I started in Memphis, pulling into town during a Biblical cloudburst. The Madison Hotel, when I found it through the curtains of rain, was a haven of dirty martinis and high thread-count sheets, but I had to wait for the dried-out morning to see Beale Street ("The Home of the Blues") in its sunlit finery.
The second most visited street in the USA after Bourbon Street, New Orleans, Beale was home in the 1900s to segregated Memphis's black culture, its banks, barbers' shops, clubs and shops. WC Handy, a Clarksdale trumpet player brought in by the mayor in 1903 as a music teacher to a local band, wrote "Beale Street Blues" in 1916, and from the 1920s to the war, every black musician, from Louis Armstrong to BB King, came to pay tribute.
The Memphis Rock 'n' Soul Museum at 191 Beale will give you the history, along with a moving evocation of sharecropper life in 1920s Mississippi. Beale Street itself, however, is now two blocks of tourist stuff between 2nd and 4th Street. The Rum Boogie Café will serve you delicious barbecue ribs, the Strange Cargo shop will sell you made-in-Korea, guitar-themed shirts for $50, but the sightseers might put you off.
You'd be better off visiting Sun Studios. Easily spotted by the giant guitar over its front door, Sun heard the first notes of rock'n'roll. In 1953, a handsome dude from Tupelo came in and asked if he could record a Connie Francis cover for his Mom's birthday. His surname was written in the book as "Prestly". You must visit Graceland, not just to check out where Elvis lived for 20 years, but to see what passed for good taste in the 1960s. The piss-elegant glassware and table settings! The African-bush décor of the living-room! The billiards room with the miles of pleated material on the ceiling!
But you must also get out of museums and on the road. I loaded up the Chrysler convertible and headed south. A few miles out, we passed the hamlet of Walls, home of "Memphis" Minnie and "Fiddlin' Joe" Martin – every one-horse town can boast some six-string nickname. Here is Coahoma, birthplace of Charlie Patton, who had (according to Howlin' Wolf) the voice of a lion, and who could, in the 1930s, play the guitar behind his back like Hendrix, or between his legs, like Chuck Berry. And here, at last, is Clarksdale, the heart of the Delta, where everyone of any consequence in Blues-land either came from or to: Sam Cooke, John Lee Hooker, Son House, Ike Turner, Big Jack Johnson, Junior Parker – and a melancholy-looking guy called McKinley Morganfield, known to blues history as Muddy Waters.
I was looking for the Ground Zero Blues Bar (its address, helpfully, was 0 Blues Alley) and here it was - a two-storey brick warehouse, seemingly disused and run-down, with doors and walls entirely obscured by graffiti. The door was locked. Just as I was thinking of finding a motel, my saviour arrived - Miss Tony, a short, cheery innkeeper, who brought me local pecan beers and showed me my room for the night. It was a suite, full of authentic 1950s furniture (in the sense that it's been there since the 1950s).
Down in the bar, the thick impasto of graffiti spreads across the counter, the pool tables and the stage. Ground Zero is internationally renowned, co-owned by the actor Morgan Freeman, an "entertainment executive" from Memphis called Howard Stovall, and Bill Luckett, a tall, Goethe-quoting construction mogul and attorney, now running for governorship of Mississippi.
Luckett and Freeman met in the mid-1990s, when both were involved in residential property. They noticed how many tourists in town were asking, "Where can we hear some live music?" "About that time," Luckett told me, "this Englishman and a Dutch guy got in touch and said they wanted to start a blues club in Clarksdale. And I thought, are we gonna leave it to people from England and Holland?"
The dark secret at the heart of the blues is displayed at the crossroads where Highway 61 meets Highway 49. Above a small traffic island, an installation of three guitars hangs in the air. It's a tribute to Robert Johnson, an artist about whom little is known; but everybody in Mississippi knows what he's supposed to have done.
He was born in 1911 in Hazelhurst, Mississippi, and worked in the cottonfields while still a boy. At 17 he married his childhood sweetheart, Virginia, but she died in childbirth. He turned to music for solace, and performed in juke joints alongside Sonny Boy Williamson and Charlie Patton. By all accounts he was rubbish. One night he walked to the Clarksdale crossroads, recited an incantation and summoned the Devil to inspire him. The devil appeared and tuned his guitar – and thereafter Johnson played like a demon.
Clarksdale isn't a pretty town, but it's fascinating to walk round. Down the main street, at 262 Delta Avenue, is the Cat Head Delta Blues and Folk Art, where you can buy arcane blues recordings and discover who's playing where that night.
Back on Highway 61, I passed no-horse towns called Alligator and Duncan, and wondered whether a diversion to Rosedale was worth a look, just because the village is namechecked in a Robert Johnson song. At the intersection with Highway 82 is Leland, which boasts murals that celebrate local stars, who include albino guitarist brothers Edgar and Johnny Winter.
Highway 61 will take you on down to Baton Rouge and New Orleans, where the music becomes Cajun zydeco and the landscape takes on tinges of French and Spanish. But it feels as if you're getting further away from the heart of the Highway, around Clarksdale. For all its ragged, juke-joint feel, the town is the uncompromising birthplace of the blues, and the highway is the concrete river which took that music north and south, turning it into jazz, rhythm and blues, and rock'n'roll. No wonder Bob Dylan felt so intense about it.