No hard-rock song has ever had a more ominous opening line: "We come from the land of the ice and snow." It was inspired by the band's concert in Iceland in June 1970, a month when the sun never fully sets. Plant started fantasizing about vikings and wrote in the voice of a Norse chieftain leading a sea invasion and expecting to die. It "was supposed to be powerful and funny," he said. Page's menacing staccato riff could scare Thor into surrendering, and Plant's Tarzan holler adds another layer of primal barbarism.