It’s not that “3D” drawing was unknown, it’s that the idea of art as being representative rather than figurative is a pretty new concept. Artists in Ancient India and Medieval Europe weren’t aiming and failing for realistic depictions, they were in a way abstracting for some aesthetic reason. The introduction of perspective in Renaissance art was controversial particularly in the context of religious art, because depicting heaven realistically blurred the line between the transcendent metaphysical world and the “real” physical world.
Latest Answers