It was exactly forty years ago today (November 8) that Led Zeppelin IV was released to the world.

IV wasn’t the official title for the album. The title was in symbols and it became known as symbols, IV and Zoso depending on who you talked to.

IV was Led Zeppelin’s biggest album, selling over 32 million units since its release. It is the third biggest selling album ever in the USA behind Eagles' Their Greatest Hits and Michael Jackson's Thriller.

Led Zeppelin started work on the album at Basing Street Studios in London in December 1970 while Jethro Tull were in another studio recording Aqualung.

Led Zeppelin recorded 11 songs at the sessions and eight made the album. The remaining three Down By The Seaside, Night Flight and Boogie With Stu were released four years later on Physical Graffiti.

The two singles released from the album were Black Dog and Rock and Roll. Australia was the only country in the world to release Stairway To Heaven as a 7” vinyl EP with Black Dog and Rock and Roll on the other side.