On their first two albums, Led Zeppelin unleashed a relentless barrage of heavy blues and rockabilly riffs, but Led Zeppelin III provided the band with the necessary room to grow musically. While there are still a handful of metallic rockers, III is built on a folky, acoustic foundation that gives the music extra depth. And even the rockers aren't as straightforward as before: the galloping "Immigrant Song" is powered by Robert Plant's banshee wail, "Celebration Day" turns blues-rock inside out with a warped slide guitar riff, and "Out on the Tiles" lumbers along with a tricky, multi-part riff. Nevertheless, the heart of the album lies on the second side, when the band delve deeply into English folk. "Gallows Pole" updates a traditional tune with a menacing flair, and "Bron-Y-Aur Stomp" is an infectious acoustic romp, while "That's the Way" and "Tangerine" are shimmering songs with graceful country flourishes. The band hasn't left the blues behind, but the twisted bottleneck blues of "Hats off to (Roy) Harper" actually outstrips the epic "Since I've Been Loving You," which is the only time Zeppelin sound a bit set in their ways.

Led Zeppelin III was something of a transitional recording for the band, marking an evolution from their early blues-based origins to the elaborately structured rock suites which would follow.

Page's love for country and cajun music, delta blues and traditional folk elements distinguishes "Gallows Pole" and underrated songs like "Tangerine," "That's The Way" and "Bron-Y-Aur Stomp" where Robert Plant's vocals begin to take on a heretofore unheard-of tenderness, while the rhythm work of Jones and Bonham reflects many non-rock elements, and Page makes telling use of acoustic string instruments like mandolin, banjo and 12-string guitar (anticipating 1971's triumphant "Stairway To Heaven").

Elsewhere, songs like "Friends" take on a darker, more experimental mood, in the manner of the late Beatles, even as the mysterious "Immigrant Song" finds the band mixing hard rock, dervish rhythms and James Brown in equal measure. And for fans of their first two recordings, there's "Since I've Been Loving You," a low, slow Chicago blues (in the manner of Fleetwood Mac's Peter Green) showcasing the good groove of Jones and Bonham, and Page's masterful lead work.