"quadratura"

(noun) - Quadratura is a term that emerged during the Baroque period to describe a type of ceiling painting (which had been going on for centuries). An artist would paint, from scaffolding, all sorts of fictitious architecture on to what was, essentially, a flat surface. The end results looked three-dimensional, and might have featured little statues in niches, ceiling ribs meeting curved walls and "openings" that allowed viewers to gaze upon the "sky". All of these illusions were rendered in perfect perspective to completely fool the eye.