Physical Graffiti is the sixth studio album by the English rock band Led Zeppelin, released on 24 February 1975 as a double album two years after the album Houses of the Holy. The band wrote and recorded eight songs at Headley Grange which, when combined, stretched the album beyond the typical length of an LP. This prompted the band to make Physical Graffiti a double album by including previously unreleased tracks from earlier recording sessions. "Physical Graffiti" was Led Zeppelin's second most commercially successful release, selling eight million copies in the United States alone.