For him, the song does not remain the same

On the Richter scale of rock, Led Zeppelin's seismic impact measures at least a 10. True, their influence on "Spinal Tap's" rock spoof scores an 11, but strip away Zeppelin's ridiculous Stonehenge stage sets and triple-necked guitars and you're left with an enduring body of music whose sales and legacy have been surpassed only by the Beatles.

It would have been easy, then, for Robert Plant to trade on his former band's glories since the band's demise in 1980. Instead, the vocalist has pursued a forward-looking solo career - summarized on a new two-disc retrospective, "'66 to Timbuktu" (Atlantic) - in which he has striven never to repeat himself. As part of that ethos, he's also resisted multimillion-dollar offers to reform Led Zep.

"An old pal of mine said, 'Hey, Robert, why do you keep turning your back on the obvious?' " says Plant in a phone interview. "Because I really love music. I don't like repetition and tedium. And he said, 'But remember, glory is fleeting, obscurity is forever.' I said, 'How much longer down the line have I to go on being either of those two conditions?' "

Plant's career has certainly vacillated between glory and obscurity. In 1998, for example, the man with the golden locks worthy of their own L'Oréal ad was selling out arenas. A year later, he found himself playing pubs, town halls, and even a zoo.

The aforementioned 1998 tour was Plant's second world tour with Jimmy Page. The vocalist had pressed the pause button on his solo career, which had already yielded five albums including "Now and Zen" (1988) and "Fate of Nations" (1993), to reunite with the Zeppelin guitarist.

Plant says that the pair weren't trying to cash in on Zep's fame. They were looking to create new and interesting music.

"The truth is that Jimmy and I did cut a collection of songs that weren't immediately commercial and didn't emulate Led Zep," recalls Plant. "We did what we'd always done, we moved along."

Page and Plant's 1998 album, "Walking Into Clarksdale," wasn't embraced by radio, or conservative audiences who looked to the duo for a nostalgic fix of the Zep days when Plant's exposed navel was more famous than Britney's.

"Here and there on that album were fantastic moments, but I had had enough of that whole idea, the great expectation," says Plant. "So I came back to the Welsh border and formed Priory of Brion, which was basically a supper act."

Priory of Brion, a band comprised of friends, spent a year quietly touring. For Plant - performing cover versions under the pseudonym "Johnny Volcano" - the anonymous Priory gigs were a chance for him to rediscover the joy of singing.

"It was the antithesis of what I'd just been doing prior to that," he says of playing restaurants in Shropshire while patrons dined on strawberries and cream. "I knew when stadium music had reached saturation point so it was just, in the end, some tired ritual. The communication with an audience and the will to create and to disturb and stimulate was at the beginning of my career, and it should be at where I was at at this point in my life."

To continue that mission, the singer convened a professional band and recorded 2002's "Dreamland," a rock album that melds delta and African blues. Over the past year, they've taken that sound from Russia to Mali's Festival in the Desert (a revelatory cut from that concert appears on "'66 to Timbuktu") to Oslo, where they played at the Nobel Prize ceremony on Wednesday. Next August, the singer says, he's likely to tour North America with Womad, a traveling world-music festival.

Before that, he has a "thunderous" album to finish. "It sounds a bit like a hip-hop version of 'Nobody's Fault but Mine.' No, no, that's not quite right," he says of the mischievous Zeppelin comparison. "It's just quite big-sounding and confident. And there's also a lot of acoustic stuff, which is trance-like and somewhere between 'Black Country Woman' and the best Malian pop."

"I want to make new music," says Plant, who says he ruefully looks at his peer group and wonders why few aspire to that goal anymore. "I want these fusions - you have to be very careful with that word - but the mélange of music. It's kept me feeling bouncy and wanting to keep going at it."