"It's very hard for people to understand how monolithic it was, looking at it today. But it was absolutely earthshaking": Was 9 February 1964 the most important day in rock 'n' roll history?

American television host Ed Sullivan (center) talks, with the members of British rock group the Beatles, on the set of his television variety series, 'The Ed Sullivan Show' at CBS's Studio 50, New York, New York, February 9, 1964. Pictured are, from left, Ringo Starr, George Harrison, Sullivan, John Lennon, and Paul McCartney. The photo was taken during prior to the group's debut performance on the show later that day.

There are shows, albums, songs that changed the trajectory of musicians' lives – they may have even inspired the dream that made them aspire to be musicians. But these are usually pockets of experiences, from hearing Smells Like Teen Spirit on the radio to being in the eye of the storm at a Sex Pistols gig in 1977. But what about impacting millions at the same moment in time? Well that actually happened once in front of an estimated 73,700 million people.

"Four guys, playing and singing, writing their own material", Bruce Springsteen wrote in his 2016 memoir, Born To Run of seeing The Beatles perform five songs on the Ed Sullivan Show on Sunday 9 February 1964. "Rock 'n' roll came to my house where there seemed to be no way out ... and opened up a whole world of possibilities."