"Perspective is nothing else than seeing a place or objects behind a plane of glass, quite transparent, on the surface of which the objects behind the glass are to be drawn." Leonardo da Vinci
Perspective in drawing and in Leonardo's works
During the Renaissance in Italy, architects and artists investigated the question of how to draw three dimensional objects on flat surfaces. They began to think of a painting as an "open window" through which the viewer sees the painted world. They also developed a system of mathematical rules, known as linear perspective, to help painters achieve their goal of realism. Leonardo learned the rules of perspective and practiced using the window as a device for drawing perspective correctly while he was an apprentice in Andrea del Verrocchio's studio.
Drawing boxes in one, two and three point perspective