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)