Cover art for Threshold's album March of Progress.
Progressive Metal was one of the earliest sub-genres of Heavy Metal music, originating in the United Kingdom in the late 1970s when Progressive Rock bands such as King Crimson, Uriah Heep and High Tide incorporated elements of Heavy Metal into their music. Heavy Metal band Crimson Glory did the opposite in 1979 and incorporated Progressive Rock into Heavy Metal. Queensrÿche and Fates Warning formed in 1982 and Dream Theater followed three years later. By 1986, these bands became the Prog-Metal equivalent to Thrash Metal's "Big Four."
Much like the instrumentation, the lyrical themes of Progressive Metal tend to be more complex, requiring and encouraging thought, and many Prog-Metal bands produce concept albums. Because of this, most Prog-Metal bands tend to favor clear and even tenor vocalists.