What tuning did Jimmy Page use for "Kashmir" and why does it sound so unique?

Jimmy Page tuned his guitar to DADGAD for “Kashmir” – a drop-D variant where the two middle strings are tuned down a whole step each. This creates a droning, open chord that rings across the fretboard, giving an ambiguous, almost modal sound with a constant low D pedal tone. The tuning allowed him to play the main riff with just one finger sliding between two positions while open strings kept ringing, making the song feel like it’s both moving and standing still. You can’t get that sound in standard tuning.