Anchored by Ritchie Blackmore's classical-tinged fret-work, Deep Purple are as heavy and rocking as Stonehenge. Initially exploring prog rock and psychedelic soul—see their blistering take on “Hush”—they hit the first of several strides with 1971's Machine Head. Thanks to their scowling riffs and bruising chug, “Smoke On the Water” and “Highway Star” redefined heavy metal. Despite undergoing extensive personnel turnover—Burn, the boogie-fuelled gem from 1974, features the piercing wail of a then young and untested David Coverdale—the band have remained true to their pioneering vision.