On the evening of December 4, 1971, Deep Purple were watching a Frank Zappa concert at the Montreux Casino in Switzerland, when someone shot a flare gun and set fire to the ceiling of the venue — completely destroying it. This served as the inspiration behind their hit "Smoke on the Water." "That was a riff I made up on the spur of the moment, in Switzerland," explained Ritchie Blackmore. "It was a case of keeping it incredibly simple. I remember Pete Townsend saying to me, 'You've got to keep things simple and take the audience with you.'" Purple were planning on recording their next album, Machine Head, at the Casino but had to move the sessions to the nearby Grand Hotel.