Tool's greatest breakthrough was to meld dark underground metal with the ambition of art rock. Although Metallica wrote their multi-sectioned, layered songs as if they were composers, they kept their musical attack ferociously at street level. Tool didn't. They embraced the artsy, bohemian preoccupations of Jane's Addiction while they simultaneously paid musical homage to the relentlessly bleak visions of grindcore, death metal, and thrash. Even with their post-punk influences, they executed their music with the aesthetic of prog rock, alternating between long, detailed instrumental interludes and lyrical rants in their songs.