Before the Renaissance, more distant objects were drawn or
painted higher on the picture plane, and smaller, but with no
less detail or color saturation. Atmospheric or aerial
perspective was not generally a part of western art until
defined during the Italian Renaissance by Leonardo da Vinci. He
called it ‘the perspective of disappearance’. "An object will
appear more or less distinct at the same distance, in proportion
as the atmosphere existing between the eye and that object is
more or less clear. Hence, as I know that the greater or less
quantity of the air that lies between the eye and the object
makes the outlines of that object more or less indistinct, you
must diminish the definiteness of outline of those objects in
proportion to their increasing distance from the eye of the
spectator." - from The Notebooks of Leonardo da Vinci (Jean Paul
Richter, 1880)