Wikipedia notes:
“Drawing inspiration (and many statues[2] and much of the marble used for construction) from the nearby Villa Adriana, the palatial retreat of Emperor Hadrian, and reviving Roman techniques of hydraulic engineering to supply water to a sequence of fountains, the cardinal created a fantasy garden. Its architectural elements and water features had an enormous influence on European landscape design.”
It is built on the side of a hill, where a river has been diverted to supply a giant cistern used to feed all of the stone fountains and waterworks. It is a true masterpiece.
It is a fantastic world that captures the imagination, and one can only believe that to visit the garden in the 1500’s would have transported the visitor to another world.