"Is this music about the jungle, Daddy?"

Thus piped up my seven year old daughter as I was driving her to school one morning, with Miles Davis' Bitches Brew brooding from the tape deck. And while any soft-headed parent would bestow precocious powers of perception upon their progeny, there's a lot to be said for the plainspeak of babes defusing 30 years worth of critical prate.

Because, yes, this music is about the jungle, daddy-o: the primordial African jungle, the cacophonous jungle that is New York City, the murky jungle of the mind. A quarter of a century before the term came to denote drum n bass (although, clocking the centipedal pulses generated by Dave Holland, Harvey Brooks, Jack DeJohnette, Lenny White, Don Alias, Bihari Sharma, Airto Moreira, Ron Carter, Billy Cobham, and Jumma Santos not so much a rhythm section as a polyrhythmic power bloc it could be postulated that these 1969/70 sessions are the original article) the Bitches Brew crew were navigating their own expedition upriver towards a heart of darkness governed by the shamanistic shadow of their Colonel Kurtz; the man they called Miles.

And, to expand upon the theme, we might assess the four-CD box set The Complete Bitches Brew Sessions, with its two hours worth of hitherto unreleased material, as Apocalypse Then The Sequel, where we see what happened to that idolatrous jungle tribe after its mad godhead was ceremoniously slaughtered by Willard. So come with me on a journey beneath the cranium and into Colonel Miles' cerebral cortex via a succession of microcosmic intros, tangled vamps, lengthy real-time jams and machete-cut edits, arriving light years later at a brain stem which houses some pretty disturbing conclusions (or 'the horror', as Joseph Conrad wrote), made most apparent in the finales of tunes like 'Pharaoh's Dance' and the title track.

Here, the rhythms of the dark continent form a live, constantly writhing matting on the bottom end of the music, an interlocking network of malevolently serpentine creepers and vines, like something out of Sam Raimi's Evil Dead (is it coincidence that the malevolent throb of 'Double Image' eventually ended up on Live/Evil?).

Indeed, from 'Miles Runs The Voodoo Down' onwards, the musicians seem to shape-shift through their instruments and adopt their own sonic anima/animus: Bennie Maupin's bass clarinet is stealthily lupine; White and DeJohnette's rhythms slither like boa constrictors; Jumma Santos skittering insectoid percussion winks in the dank dark; John McLoughlin's spiky-backed guitar gnaws on sun-bleached bones; Brooks' bass is a horribly slow and bad-tempered reptile bellying along the riverbed; Joe Zawinul, Larry Young and Chick Corea's electric pianos glisten like will o the wisp, and above this delicately balanced eco-system, Miles' wailing trumpet soars, swoops and shrieks like a great prehistoric bird. Bitches Brew is the sound of a dark cauldron a-bubbling deep in the thicket, a voodoo gumbo where all the players throw their amulets and charms into the stew and then bring it to boil over the fissioning fisson of their improvisatory skills.

The material that makes up The Complete Bitches Brew Sessions was recorded over eight dates between August 19th 1969 and February 6th 1970, in Columbia Studios B & E, New York City (the six original Bitches Brew tracks were culled only from the first three dates, August 19-21).

Miles characterised the tone of these sessions as loose and tight at the same time. It was casual but alert, everybody was alert to the different possibilities that were coming up in the music. "While the music was developing I would hear something that I thought could be extended or cut back. So that recording was a development of the creative process, a living composition. It was like a fugue, or motif, that we all bounced off of."

The source material came from Miles' own compositions, plus those of Wayne Shorter, Joe Zawinul and, in the case of 'Guinnevere', David Crosby. But despite the fact that this was as much an ensemble recording as any of those taped with John Coltrane, Cannonball Adderley, Bill Evans, Paul Chambers and Philly Joe Jones, Davis strictly co-ordinated the whole endeavour, and resented later suggestions that the album was the brainchild of Columbia president Clive Davis, who was eager to present Miles to a whole new audience besotted with the cosmic experimentation of The Grateful Dead, Santana and Jimi Hendrix. True enough, Miles felt that jazz had grown stagnant, and was looking to break through to a rock audience, but only on his own terms.

So while Bitches Brew was light years away from the mind-bending big-band music of Miles Ahead, the molten extemporisations of Milestones, or the grand visions of Sketches Of Spain, it wasn't as divorced from his past as disgusted purists would insist. Here, Davis was in fact recreating the fever-in-the-funkhouse swelter he first encountered in Harlem 25 years earlier.

"It was just like one of them old time jam sessions we used to have up at Minton's back in the old bebop days," he would recall. "Everybody was excited when we all left there each day. What we did on Bitches Brew you couldn't ever write down for an orchestra to play. That's why I didn't write it all out, not because I didn't know what I wanted; I knew what I wanted would come out of a process and not some prearranged shit. This session was about improvisation, and that's what makes jazz so fabulous."

Before Bitches Brew, the jazz menagerie might ve agreed that Miles, like Joyce, created only masterpieces, but in its wake, the hardliners slapped him with the same Judas writ the folkies had recently served Bob Dylan. Elsewhere, the moderates lukewarmly offered that the album was a Rubicon the master had to cross, but it was predominantly young rock and funk aficionados who embraced it from the jump.

The most remarkable aspect of the new music was that Miles, having redefined his chosen genre with Bird, Coltrane and Evans, was willing to reassess his approach from the point of view of a disciple, not a master, integrating the sounds of the street into what he d learned from cool jazz, be-bop, hard-bop and classical styles. This was the man who had made Kind Of Blue arguably the greatest jazz album ever deciding not that the old forms had grown tired, but that he was tired of them, and so this vamper needed fresh blood.

But the reality is that the fusion (r)evolution didn't start with Bitches Brew: Davis had been heading this way for at least five years, and would continue on the same path for another five. After a period of semi-retirement that lasted from 1960-63, the turning point came with the arrival of a brilliant rhythm section; Herbie Hancock, Ron Carter and Tony Williams. These players, along with tenor saxmasters like Wayne Shorter and George Coleman, expanded Miles' vision to include funk, rock, soul and the experimentations of Ornette Coleman.

After the astrophysical mid-60 s explorations of albums like ESP, Miles Smiles, and Filles De Kilimanjaro came the classic In A Silent Way, with Davis transposing Duke Ellington's orchestral manouevres into quintet format. Then, barely six months later, the Bitches Brew sessions. Still steaming over the fact that the killer Silent Way line-up of Shorter, Corea, DeJohnette and Dave Holland, which had toured from Spring of '69 right up to August, hadn't been preserved for posterity ("Man, I really wish this band had been recorded live because it was really a bad motherfucker . . . but Columbia missed out on the whole fucking thing,"), Miles insisted on documenting all the lightning chromosome shifts that were taking place in the studio that fall/winter, instructing engineer Ted Macero to concentrate on getting everything on tape, leaving the suits to sort out the release schedules.

A wise strategy too, for this music was mutating by the minute. (To that effect, witness the difference between both versions of 'The Little Blue Frog', a jam recorded on November 28th 1969. The first take fairly ripples with feral grace, but by the second, the DNA of the tune has already skipped several dozen generations, its genetic message well and truly scrambled, resulting in a warped musical polymorph.)

But quite apart from the social and societal factors at work on Bitches Brew (and it's worth pointing out that the recording process began approximately 30 hours after Hendrix infamously exploded 'The Star Spangled Banner' at Woodstock), advances in technology afforded Davis a new methodology. Previously, he had tightrope-walked a median between polar opposite techniques; either complex orchestration (albeit based around sketches the players often didn't get to see until they entered the studio, as in Kind Of Blue) or else advanced improvisation. But here, instead of selecting the best takes in their entirety on merit of the players individual heat, he and Macero began utilising complex editing and looping techniques; cutting, splicing and reconstructing arrangements after the fact, then electronically treating the resulting collages.

Furthermore, Davis horrified many of his disciples by distorting and distending his famously torch-like trumpet tone with octave dividers and echoplexes, as well as playing through an amp (from 72 to 75 he would almost exclusively favour a wah-wah-pedal). In fact, the whole band were in on the technology, with guitar and keyboard departments utilising ring modulators, fuzzboxes and all manner of sound-altering gizmos. These developments offered Davis the arranger a consciousness-expanding variety of sonic options sometimes he edited so abruptly as to jar the groove to a shocking, almost heretical extent and the process that birthed Bitches Brew came to be regarded as cutting edge.

The cache of nine unreleased tracks on The Complete Bitches Brew Sessions (plus several more that turned up on albums like Live/Evil, Big Fun, Circle In The Round and in edited form as singles) are a yardstick of Miles and the band s creativity at this point. Much of this unheard material is little short of spellbinding, like putting your eye to a rip in the fabric of the universe and seeing another thousand pair of eyes peering back at you. On tracks like 'Trevere', 'Feio' and 'Yaphet', the introduction of Khalil Balakrishna's sitar and Bihari Sharma's tamboura and tabla lend the whole soundscape a Byzantine air, yet the percussive call and response routines are intrinsically African, even hip-hop at the core.

It's been suggested that these recordings constitute a blueprint for world music, but if anything, they're closer to out-of-this-world music (even the jazz-rock fusion label won't stick, because even in its most abstract mutations, rock rarely sounded as far out as this). And if the original cover illustration with its three god-like Nubian figures gazing westward presents Bitches Brew as an homage to Africa, it might also allude to Dali's false memory of the continent, portrayed in his 1938 work Impressions Of Africa, depicting the artist obscured by his palette, one paranoid eye glaring out from the canvas.

So it's an exile's record, the love-song of a black man in New York. Indeed, Carlos Santana has opined that Bitches Brew throbs with the sound of New York City, the cabs, the canyons of buildings, the people, and all the city's energy and excitement. Miles biographer Quincy Troupe later echoes this in his sleeve notes, testifying that, "it's eerie the way this tune ('Pharaoh's Dance') hits me and kind of invades my senses with this feeling of Manhattan traffic". Other influences included the women in Miles' life at the time – hence the album title – not least of all Devon, who introduced him to Jimi Hendrix (the man and the music tales of lost recordings of jam sessions between the two legends would persist for decades), and Betty Mabry, who swayed Davis' sartorial sensibilities from starched suits to loose, ethnic but elegant garments. Here the musician was reconnecting with an ancient black-archangel heritage through the sounds of the tenements, but still incorporating lessons learned from Dizzy and Duke.

Writing for Down Beat magazine in 1983, black cultural analyst and all-round hipster Greg Tate asserted that, with Bitches Brew Miles crossed over the threshold of bebop into Sly and Jimi's stereovision New Jerusalems. "(It) is an orchestral marvel because it fuses James Brown's antiphonal riffing against a metamorphic bass drone with Sly's minimalist polyrhythmic melodies and Jimi's concept of painting pictures with ordered successions of electronic sounds. Bitches Brew can also be heard as a devilishly Milesish takeoff on John Coltrane's spiritual energy music and that music's saxophone, percussion and bass batteries, modal improvs, tone clusters, and cosmic yearnings, thus making the double-set rank as an act of comic blasphemy with Richard Pryor's Preacher routines or with certain African genesis myths in playing prankster with God's tongue by dragging the heavens back into the province of the vernacular namely the streets and the language of the streets: sermons made scatologies which find their musical parallel in what funk did to gospel."

Despite horrifying many of the jazz police upon its release in 1970, Bitches Brew sold 500,000 copies, but like all classic records, its doppler effect has far exceeded the sales figures. Within a relatively short time-span, the personnel on these eight sessions went onto distinguished careers with Weather Report, Herbie Hancock's Mwandishi Band, Return To Forever, John McLoughlin's Mahavishnu Orchestra, Circle and Stone Alliance. Eventually, this music would have a serious impact on acts as diverse as Public Enemy, Tricky, Living Colour, PiL, Radiohead (check out the Fender Rhodes piano on 'Subterranean Homesick Alien'), Spiritualized, Primal Scream, Massive Attack and dozens more. Indeed, Harvey Brooks' lethally simple Fender electric bassline on Bitches Brew suggests a prototype of the kind of sub-aquatic dub that can be found all over Vanishing Point or Mezzanine.

If there's any reason to venerate musicians over government ministers, car salesmen, priests, kitchen porters and the man on the street, it's that occasionally, on works like The Complete Bitches Brew Sessions, they exhibit the ability to transmit magic. As the century draws to an end, anoraks everywhere will be compiling their lists of the most influential and powerful musicians of the last 2000 years. Alongside Coltrane, Duke, Mozart, Beethoven, Hendrix and Stravinsky, Miles'll be there, bad and beautiful as ever.