The power of this music is its grasp of rhythms that, as if emulating the walk of a person with focused mind and goal in sight, drive forward in marginally increasing mathematics but by maintaining a drive allow the band to augment it through repetition, in the classic doom style gaining intensity through ongoing ambiance; layers fall together slowly and in the cycling re-iteration become both more normalized and prominent. Slayer, along with Hellhammer and Bathory, essentially invented the sound of modern underground metal by combining the drum-independent guitar phrases of hardcore with the structured riffing and songs of NWOBHM, producing a ferocious new sound that addicted all who encountered it.