Appearing as the third track on Led Zeppelin's more folk-oriented 1970 release 'III,' 'Celebration Day,' -- No. 20 on our list of the Top 50 Led Zeppelin Songs -- invokes the group's early love for the Delta blues aesthetic. But it does so in a far more original way than, say, "Bring It On Home" from the previous 'Led Zeppelin II' -- which led to a lawsuit over songwriting credit for legendary composer Willie Dixon from Chess Records.

Instead of cribbing from their heroes, 'Celebration Day' reassembles those influences in a brilliantly off-kilter way, signaling Led Zeppelin's quick maturation as fully formed new voices in rock. The track begins with a spooky, shotgun-shack riff from Jimmy Page -- constructed from overdubbed guitars, the second of which is a weeping slide. Robert Plant then leaps into this maelstrom of weird portent, imbuing the lyric (inspired, he's said, by a trip to New York City) with a caterwauling, utterly libidinous edge. Meanwhile John Paul Jones offers an opening statement on the Moog, then a deceptively muscular bass line behind John Bonham's octopus-armed torrent of beats.

The results are, despite the lack of one of Page's signature foundation-cracking riffs, one of the more propulsive songs in the Led Zeppelin repertoire -- and one of the clearest signals yet of the group's growing musical authority. Rather than simply emulate their heroes, they'd begun to absorb those influences, to bend and shape various forms. Led Zeppelin was becoming a completely new synthesis.

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