A series of tiers were built, with terraces on every level. The gardens probably didn't actually "hang" but the walls were overhung with cascading vines and plants.
The Hanging Gardens of Babylon are the only ancient wonder that has not been verified through archaeological means. It is thought that the gardens were destroyed by an earthquake in the second century BC.
I wonder if Amytis was comforted by the site of this artificial green mountain rising from the flat plains?