On this date 49 years ago, King Crimson wowed the 650,000 strong crowd in London's Hyde Park. Supporting The Rolling Stones, the gig played in pivotal role in establishing Crimso at an early point in their career.

When Crimson took to the stage they restricted themselves to a truncated set consisting of 21st Century Schizoid Man, In The Court Of The Crimson King, Get Thy Bearings, Epitaph, Mantra, Travel Weary Capricorn and Mars.  Dik Fraser recalls that during the opening number a large framed photograph of Brian Jones fell, almost catching Greg Lake. The bass player shrugged off the mishap, but several people backstage thought it was some kind of augury or supernatural manifestation.

It was a good day for Crimson, however. The newest member of the road crew, Richard Vickers (better known as Vick), recalled in his memoir of that period: "The high point of that gig was the whole audience rising to their feet as one and cheering Ian McDonald solo during ‘Schizoid’ — I remember the hairs on the back of my spine rising in unison as the roar from this huge crowd went up."

In the crowd stood Jamie Muir. Having only recently moved down from Edinburgh, the future Crimson percussionist was then playing with free improvisers such as John Stevens and Derek Bailey. He was impressed by the force Crimson created. "What was incredible was that they just exploded on to the scene fully matured. Most bands come along and then develop but Crimson just came on and exploded with this very adult, intelligent, cutting-edge music. It was just this whole package that went wallop!"

Fourteen-year-old Trevor Lever, attending his first concert, found Crimson perplexing. "At one point I thought an orchestra was playing but through my binoculars saw only four blokes on the stage. ’Where’s the orchestra?’ I asked a mate. ’Dunno,’ was the informed reply. ’Who is this playing?’ I said to no-one in particular. ’King something,’ I was told. I made a mental note to check this band out at a later stage." It was the start of a love affair with Crimson which Lever — who has seen shows by every incarnation of the band since — continues to this day.

Crimson finished as usual with “Mars” (complete with an air raid siren being cranked up from underneath the stage by Enthoven and Fraser). Enthoven, celebrating his 25th birthday that day, regards this as the defining moment of the launch of King Crimson. McDonald agrees that it was the point at which Crimson arrived, but adds: "It would sound blasé to say that this was just another gig for us, though in a sense it was; we were having a great time discovering and enjoying our music, but we were also experienced enough individually not to be too greatly affected by any particular venue."

For years it was assumed that there was no footage of Crimson other than a brief glimpse of an off-stage Fripp peering at Mick Jagger through the potted plants on the Stones In The Park DVD. Minutes later, Fripp and other KC members were unceremoniously thrown out of the back stage area.