Sometime during the week of August 12, 1968, the band that would take over the world as Led Zeppelin rehearsed for the first time in a central London basement.
The coming together began when Yardbirds guitarist Jimmy Page found himself without a band when three members abruptly quit.
With a Scandinavian tour booked, Page and manager Peter Grant united bassist/keyboardist John Paul Jones with two other 20-year-olds from the British Midlands - singer Robert Plant and powerhouse drummer John Bonham.
Initially Page wanted Terry Reid - who he spotted as an opening act on a Rolling Stones tour in 1966 - to sing with B.J Wilson on drums.
But as the new quartet launched into the R&B chestnut and Yardbirds staple "Train Kept A'Rollin'" in that basement, the chemistry, according to all four members, was instant.
"We first played together in a small room on Gerrard Street, a basement room, which is now Chinatown," Jones recalled in 1990, according to the band's website.
"There was just wall-to-wall amplifiers, and a space for the door -- and that was it. Literally, it was everyone looking at each other, 'What shall we play?' Me doing sessions, I didn't know anything at all. There was an old Yardbirds' number called 'Train Kept a Rollin'.' The whole room just exploded."
"I could feel that something was happening to myself and to everyone else in the room," Plant remembered.
"It felt like we'd found something that we had to be very careful with because we might lose it, but it was remarkable -- the power."
No recordings of the rehearsal have ever surfaced and that first song - which would be the group's live opener for most of its first year of existence as well as its final 1980 tour - was never properly recorded.
From that first rehearsal the band's ascent escalated quickly.
Their first show in the UK was on October 4 at the legendary Marquee rock club. By the end of that month the band's name had become Led Zeppelin. A deal with Atlantic Records was signed in November. And by December 26 a US tour was announced and an album was released in January.
Led Zeppelin played 145 shows in 1969 and by the end of the year released the blockbuster "Led Zeppelin II" (featuring their breakthrough single "Whole Lotta Love") and headlined venues like London's Royal Albert Hall, New York's Carnegie Hall, the Boston Garden and Detroit's Olympia Stadium.
Led Zeppelin went on to become one of the most popular rock bands in history, dominating the 1970s, influencing countless thousands of musicians and, according to unofficial estimates, selling more than 200 million albums worldwide.