Through it's not their first album -- that would be 'This Was,' from the year before -- 'Stand Up' represents the moment when Jethro Tull was born. Released on Aug. 1, 1969, this project found Ian Anderson molding the band's sound to reflect his personal, highly original and idiosyncratic musical vision.

Before, Anderson had collaborated more extensively with now-departed guitarist Mick Abrahams on 'This Was,' and even had a brief partnership with Black Sabbath guitarist Tony Iommi, in early '69. As Anderson began to fully assert his leadership, however, Jethro Tull headed down the path towards progressive rock greatness.

Indeed, a single listen to 'Stand Up' is enough to marvel at its confident eclecticism, one that saw Anderson taking inspiration from numerous sources: Led Zeppelin for the post-blues heavy rock riff-crunch of 'A New Day Yesterday,' 'Nothing is Easy' and 'For a Thousand Mothers'; Roy Harper for the eccentric folk stylings of 'Look into the Sun' and 'Fat Man'; and everything at once on 'Back to the Family' and 'We Used to Know.' Elsewhere, there were even more exotic experiments in classical (the beautifully scored 'Reasons for Waiting'; Bach's rearranged 'Bouree') and world music (see 'Jeffrey Goes to Leicester Square,' where Anderson plays a Russian 'Balalaika').

New guitarist Martin Barre, who'd eventually become the only consistent member of Jethro Tull's ever-evolving lineups over the years, joined a standing rhythm section of Glenn Cornick and Clive Bunker in creating this whirlwind of sound. Through it all, the only consistent threads were Anderson's quirky, elliptical lyrics, distinctive vocal affectations (worlds away from his tentative croon on 'This Was') and, of course, his ever-more present flute -- which soon became a signature part of the Jethro Tull legend.

Fans responded, sending Jethro Tull to the top of the U.K.'s album charts for the first time. 'Stand Up' also reached the American Top 20, signalling a new era of creativity and success. Seven straight Tull albums, beginning with this one, would reach at least gold-selling status in the U.S.

Listen to Jethro Tull's 'Stand Up'