When U2's No Line on the Horizon arrived on March 3, 2009, more than four years had passed since the Irish rockers had released their previous album, How to Dismantle an Atomic Bomb, marking the longest period between studio releases for the band at the time.

U2 had started working on Horizon in 2006 with producer Rick Rubin, but the group soon abandoned those sessions and reconvened in May 2007 with longtime collaborators Brian Eno and Daniel Lanois. Another of the band's producers, Steve Lillywhite, also was brought in to work on some tracks. Writing and recording for the album was done in the U.S., the U.K., Ireland and Morocco, with the music of the latter country influencing the sound of some of the tracks.

How to Dismantle an Atomic Bomb and its predecessor, 2000's All That You Can't Leave Behind, had, for the most part, seen U2 returning to its classic sound of the '80s, but Bono and the band had intended for No Line on the Horizon to mark a new direction for the band.  How successful they were at achieving this is open for debate.

Some songs certainly feature sonic experimentation -- drums loops, samples and synths -- but much of the material sounds is if it could have fit in well on either of U2's previous two records.  First single "Get on Your Boots" was a fast-paced and infectious tune that recalled the How to Dismantle hit "Vertigo," while the soaring and melodic second single "Magnificent" brought up such early classics as "New Year's Day" and "Pride (In the Name of Love)."

No Line on the Horizon debuted at the top of the Billboard 200 and went on to be certified platinum after selling more than a million copies in the U.S., although it ended being considered a commercial disappointment. Of the three singles released from the album -- "Get on Your Boots," "Magnificent" and "I'll Go Crazy If I Don't Go Crazy Tonight" -- only the first cracked the Top 40 of the Billboard Hot 100, reaching No. 37.

While No Line on the Horizon may not have had the impact U2 had hoped for, the ensuing tour the band mounted to support it certainly did. The U2 360 Tour, which featured a massive, futuristic set, ran from June 2009 to July 2011. It became the most successful trek of all time, grossing more than $736,000,000.

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