In the early 15th century, the Florentine architect Filippo Brunelleschi achieved one of the most radical conceptual breakthroughs in the history of visual arts. Throughout the Middle Ages, painting depicted objects and figures according to their religious or hierarchical importance rather than their mathematical spatial relationships. Brunelleschi discovered a way to geometrically reproduce how the eye perceives the world on a two-dimensional surface, designing a famous optical experiment in front of the Florence Cathedral (Duomo) to prove it.

Standing at the main portal of the cathedral, directly facing the Florence Baptistery (Battistero di San Giovanni), Brunelleschi made a small painting of the baptistery rendered in precise linear perspective on a wooden panel. He then drilled a small peephole through the panel at the exact vanishing point. A spectator would look through the back of the panel via this peephole while holding a mirror in their other hand in front of the painting. By adjusting the mirror, the viewer would see either the painted representation or the actual baptistery behind it. The painted lines lined up so perfectly with the real building that viewers struggled to tell the two apart. Brunelleschi even applied a burnished silver leaf to the sky portion of the panel to reflect the actual sky and moving clouds, enhancing the illusion of reality.

This experiment provided the first empirical proof of single-vanishing-point (linear) perspective. Brunelleschi established the geometric rule that all parallel lines receding into space must converge at a single 'vanishing point' on the horizon. This mathematical system was codified in 1435 by the humanist scholar Leon Battista Alberti in his treatise 'De Pictura' (On Painting), providing the fundamental framework that would define European painting and architecture for the next five hundred years.