One of the great recordings. A time capsule entry for the human race.
This is technically blues music. So much about the verse is blues, the guitar part, the vocal pattern.
But what blues group ever let their drummer record their part in the bottom of a stairwell? What blues song ever had a heavy, syncopated drum beat like that at all?
And beyond the verse, the song completely leaves all definition behind. The "chorus" is a pure instrumental that fuses one of my favorite guitar progressions with the grooving bass guitar of John Paul Jones. I will never forget the goosebumps I felt the first time I heard this chorus, at home with my brother, digging into this record the night I decided to take my first deep dive into my bro's Led Zeppelin collection (the same night as I heard "Immigrant Song," to reference back a bit). The middle development, with its organ, emphatic singing, thundering drums, and complimentary guitar, is just part of my consciousness - I take its perfect composition as just a given. I don't throw around the word, but Led Zeppelin has a genius that allows you to relax into a sound sponge, like watching a transcendent athlete continue to perform again and again, never saddling you with uneasiness that they'll choke in the clutch.
Robert Plant is credited as a great stand-alone vocalist. But in "When the Levee Breaks," he is a full instrumental contributor, opening this song with a hell of a tranced-out harmonica solo, then adding another beaut in the middle where the standard Jimmy Page guitar solo should go. His harmonica work was never perfunctory, not just some frontman affectation. When he decided to add harmonica, he always contributed sonic memories claiming part of our collective unconsciousness on their own merits. By comparison, John Lennon in the early Beatles records played harmonica like it was a novelty. There are some famous Beatles harmonica cues, but they are brief sound bites, and by the later records, the harmonica was gone entirely. Robert Plant righteously wailed on that instrument.
Just listening to the sound of the song, there are so many details in the recording, such attention to the panning of the instruments (and the panning slowly moves around throughout the song too), such attention to the effects on all the instruments, nothing sounding exactly natural. The entire track was recorded and then slowed down, creating that overall deep, gravely feel. I'll never quite understand how Jimmy Page got his guitar voice to be essentially clean but with an indefinable hoarseness. The cymbal sound in the drums was always so broad and sustained, even when not recorded in a stairwell, creating this kind of classical weight.
Many bands can go out and jam on a stage for seven minutes and be very impressive. Very few bands can compose a song that does enough in melody, structure, and sound production to hold interest for seven minutes. "When the Levee Breaks" is a heavyweight song from a heavyweight band.