Mitra Ardron - Permaculture How To Build a Herb Spiral

Mitra Ardron - Permaculture How To Build a Herb Spiral: "You'll need: 1-1.5 m3 of rock, more in a humid climate; 1/4 - 1/2 m3of compost; 20 or 30 herbs; A small amount of cardboard; Friends with strong backs"
Something like this?
Actually I dont really get this... Help!