I was listening to a song by Blue Oyster Cult and recognized part of “Rhapsody on a Theme by Paganini.” Granted, that was a very popular composition among rock guitarists at the time, but I had to grin. They also slipped in a bit of “Hall of the Mountain King” in a different piece. Classical music appears a lot more than people would think, once you really listen carefully. Bach, of course, and Sabaton uses Bach at least once per album, or so it feels. Orff’s Carmina Burana and the tune of the “Dies Irae” are also found in many places.
It’s intriguing how rock borrows from classical and liturgical sources. Soundtracks are (in)famous for it, and Basil Poledouris got into legal trouble for the original Conan score. Why John Williams didn’t get in similar trouble I’m not sure (both borrowed from Holst). The invention of the leitmotif by Wagner was a boon for later generations of composers. But to pull entire patterns and chunks of a composition . . . You don’t have to dig very deep into many rock-song writers’ backgrounds to find at least a basic education in the western musical canon. They have that tool in their toolboxes, and know what is available to fit the sound they want.