In 1968, the Stones, acting on a suggestion by pianist Ian Stewart, put a control room in a van and created a mobile recording studio so they would not be limited to the standard 9–5 operating hours of most recording studios. The band lent the mobile studio to other artists, including Led Zeppelin, who used it to record "Led Zeppelin III" (1970) and "Led Zeppelin IV" (1971). Deep Purple immortalised the mobile studio itself in the song "Smoke on the Water" with the line "the Rolling truck Stones thing just outside, making our music there".