Led Zeppelin's reflective, pastoral third album opened somewhat ironically with 'Immigrant Song' -- one of the group's most straightforward hard rock anthems, which falls in at No. 23 on our list of the Top 50 Led Zeppelin Songs.

Inspired by a Zeppelin tour of Norway in 1970, the song opens from silence into a staccato guitar/bass/drum riff that was among the heaviest the group ever recorded, with Robert Plant wailing a wordless Viking war cry over the top. The lyrics are drawn from legends of Viking hordes invading new lands, and inspired the title of the salacious Zeppelin biography, 'Hammer of the Gods.'

Incongruously among Zeppelin's heavier tracks, 'Immigrant Song' was a straight rhythm track with no guitar solo -- which may help explain its release as one of Zeppelin's few singles, landing in the Top 20.