By the mid-60s, jazz was floundering. The preceding decade saw bebop – the most radical post-war interpretation of the breed – birth several pioneering sub-genres. This reinforced the forward-looking credentials of the artform whilst rendering it increasingly mainstream behind the idyllic picket fences of White America. But the noble experiment had faltered badly.

Kind of Blue, the best-selling jazz album to date, emerged just before Ornette Coleman released The Shape of Jazz to Come, shaking the foundations of the genre. The resulting free jazz ascendancy disregarded convention and favoured the avant-garde, alienating numerous listeners while catalysing the acceptance of rock ‘n’ roll as the foremost contemporary US musical genre. Many appreciate free jazz, but British audiophilesm, for whom accessible, homegrown straight-ahead jazz was increasingly popular, would not know how to describe the characteristic cacophony of the new sub-genre until The Clangers premiered ten years later.

With jazz no longer at the cutting edge, the art form succumbed to stagnation and short-lived fads. The distinctive Austin Powers theme, ‘Soul Bossa Nova’, a foot-tapping 1962 Quincy Jones instrumental, represented ephemeral trendiness as opposed to timeless cool. Rather than assimilating Brazilian music to advance their genre, jazz labels released successive samba-infused albums to exploit fashions and distract casual listeners from the avant-garde barrage. Of the three main jazz schools – hot, cool and “is this just tuning, or has it actually started?”, the latter camp was winning. Something had to change.

Enter, shrouded in mystery and cigarette smoke, genius trumpeter Miles Davis: original Prince of Darkness, tireless innovator, and celebrated Kind of Blue architect. Between 1968 and 1972, Davis recorded a seminal tetralogy which returned jazz to the forefront of musical innovation. He birthed the crossover jazz-rock genre and assembled players who later formed five of the most important but underappreciated 1970s bands of all time.

Fittingly released only six days after the Apollo Lunar Module finally landed, the ethereally beautiful In a Silent Way would probably be considered space-age music by listeners of Dave Brubeck or Bill Evans. The album became a significant influence on the genre, punctuated by an exquisite Joe Zawinul melody, and even an accidentally-toppled beer bottle. Twice.

However, the real shock was Bitches Brew. Every aspect of the double LP (including the bold title and surrealistic gatefold sleeve), suggested a thoroughbred musical statement. Abrasive trumpet blasts, aggressive tape edits, and a dense rhythmic backdrop jointly created a difficult but rewarding listening experience. With this album, Davis completely eschewed established musical forms while moving far beyond free jazz.

The next major release, Jack Johnson, fused the desire to create the greatest rock band in existence with a tribute to the famous pugilist and an exploration of African-American identity. Yorkshire-born guitarist John McLaughlin battled Davis for prominence across the first part of the album, before more melancholy and meditative atmospheres take hold. Boxing seems to permeate the LP, influencing the subject matter and confrontational musical delivery.

Then came one of the most controversial jazz statements ever. On The Corner aimed to return the genre to Black America, drawing on the infectious funk of James Brown and even the stark experimentalism of Karlheinz Stockhausen. Ultimately, the mixture of visceral groove and constricted improvisation baffled critics; upon release, the album sold poorly. However, its reputation has improved dramatically, and the work is now cited as a major influence on jungle and hip-hop music.

After On The Corner faded into obscurity, Davis focused increasingly on live performance before commencing five years of sex and drugs, yet remarkably little rock ‘n’ roll. Though he would return in 1981, later collaborating with multi-instrumentalist Marcus Miller for Tutu, arguably the foremost 1980s jazz album, he ceased to be regarded as an important innovator. However, young drummer Tony Williams had formed fusion-group Lifetime after the 1969 In a Silent Way sessions. It became the first of five major jazz-rock acts founded by Davis alumni, particularly the Bitches Brew team, which would define the sub-genre in the 1970s.

Another Davis drummer, Billy Cobham, formed The Mahavishnu Orchestra with John McLaughlin in 1971. The hard-edged international group drew on Indian classical music and progressive rock, releasing some of the heaviest canonical jazz albums. Following his Scientology conversion, keyboardist Chick Corea collaborated with Lenny White in Return to Forever, an accessible Latin-infused band with a widely varied output. Herbie Hancock, another esteemed keyboardist, released two albums with The Headhunters, using the fundamentals of On the Corner to create a more approachable brand of jazz-infused funk. Davis even opened for Hancock, which doubtless irritated the experienced trumpeter, yet was the first evidence of the baton being passed on.

Perhaps the greatest of all these groups was Weather Report. Core members Wayne Shorter and Joe Zawinul recorded fifteen albums from 1971 to 1986, forming the backbone of 1970s jazz-rock. From the tentative experimentation of the promising debut to the raw power of Mysterious Traveller and sheer joy of Heavy Weather, the ensemble blazed a trail of unmatched virtuosity and innovation. The notion of a well-known jazz act filling arenas, headlining Glastonbury and releasing a double LP of greatest hits appears strange, but Weather Report were no ordinary band.

Similar to the closely-related progressive rock, jazz-rock ‘fusion’ capitulated to punk and changing tastes as the 1970s ended. Yet, fusion was also a victim of its own success: aiming to reach the widest audience, record producers began infusing the sub-genre with vocals and disco beats, ultimately gaining few appreciators. Furthermore, the warm ambience of jazz label CTI later inspired smooth jazz which, though not without initial artistic value, eventually swamped countless radio stations with unashamed cheesiness. But the underappreciated jazz-rock vein remains ripe for musical exploration.

Fusion might leave rock fans bemoaning the presence of a saxophone line and jazz enthusiasts horrified by prominent guitar solos. However, music should not be placed into such boxes and judged according to its degree of conformity to genre conventions. The 1970s jazz-rock explosion arguably produced some of the most forward-thinking albums of all time, many of which stemmed from the likes of Bitches Brew. Also notable is British fusion – involving great bands including Nucleus, Brand X and Earthworks – and the partial revival of the sub-genre under GRP Records. But new listeners wanting to explore this rich history are advised to take the long road, following the knotty branch connecting In a Silent Way to Heavy Weather, undoubtedly discovering hidden gems along the way.