According to mainstream pop-music history, hard rock and disco were mortal enemies in the late 1970s. The former perceived the latter as overly effeminate and in many cases explicitly gay; the latter dismissed the former as macho and homophobic. It's a relationship best exemplified by the infamous Chicago disco riots. In the summer of 1979, disco haters -- most of them lunkheads who had little understanding of rock 'n' roll's tangled history beyond stereotype and myth -- gathered at Comiskey Park during a White Sox game and voiced their displeasure with the trend by participating in a record-burning bonfire, one that quickly devolved into a spat of random violence and vandalism.
However, if we rewind a few years more, back to the first half of the decade, the relationship between the two subcultures was significantly different. In its earliest stages, beyond a few main characteristics (howling diva vocals + saccharine strings + incessantly pounding beat), disco wasn't a genre of music per se; it was more of a philosophy of how to make urban club-goers shake their asses all night long. Profoundly inspired by the concert-as-epic-dance-party concept that acid-rockers and hippie groups such The Grateful Dead and The Allman Brothers Band had innovated on the ballroom circuit, a string of DJs in New York (among them Francis Grasso, David Mancuso, Nicky Siano and Walter Gibbons) devised methods of mixing and blending music that allowed these disco pioneers to craft long, uninterrupted flows of sound rather than a collection of discrete tracks.
These DJs, who spun records in many of New York's most hardcore gay dance clubs, were lovers of rhythm & blues, funk, Latin music and soul the foundations of what would become disco the genre, in other words. However, they also dug a lot of hard rock, or at the very least culled a large stock of breakbeats from its ranks. Bill Brewster and Frank Broughton's book Last Night a DJ Saved My Life: The History of the Disc Jockey contains numerous passages that help shed light on this open-sourced and very freewheeling time in sonic exploration. There's one in particular, which can be found in the section on Grasso (pages 132-137), that really stands out:
Another of his signature mixes was a blend of Led Zeppelin's "Whole Lotta Love" with the drum break from Chicago Transit Authority's "I'm a Man." He sent Robert Plant's primal moans surging over the top of a sea of Latin percussion. The dancefloor mirrored the music's ecstatic rite and reciprocated with cacophonous wails. In addition to Zep and Chicago (as Chicago Transit Authority eventually came to be called), Grasso and his peers also played a lot of Santana, Steve Miller Band, Rare Earth, James Gang and Grand Funk. What all these bands had in common, interestingly enough, is a profound love for hard funk and/or jazz fusion. In fact, most of them had shared a stage or two in the early 1970s with Sly & the Family Stone, Funkadelic and even Miles Davis' electric bands, from whom they learned much about the art of the syncopated groove.