4. 'Kashmir' (1975)
It's their hugest-sounding track, partly because it was one of the few that used outside musicians – a string and brass corps that augmented Jones' Mellotron swirls, Bonham's druid storm-trooper processional and Page's Arabic-Indian vibe ("I had a sitar before George Harrison," he said). Plant's lyrics were born from an endless car ride through southern Morocco, and his 15-second howl around the four-minute mark may be his most spectacular vocal moment. Plant called it "the definitive Zeppelin song."