Drawing from Treatise on Perspective by Du Cerceau
Drawing from Treatise on Perspective by Du Cerceau, Soane Museum Library
This is from a book on how to draw perspectives called Leçons de perspective positive by Androuet du Cerceau (1510-84), first published in 1576. Perspective is the art of creating a picture of an object, often a building, which comes very close to the impression of reality, although it is on a flat surface.
Think of how railway lines, which are really parallel, appear to meet at a point in the far distance, called the vanishing point. This is because objects appear smaller as they get further away from you. When drawing in perspective it is important to establish where the vanishing point is.