Geometry... is of much assistance in architecture, and in particular it teaches us the use of the rule and compasses, by which especially we acquire readiness in making plans for buildings in their grounds, and rightly apply the square, the level, and the plummet. By means of optics... the light in buildings can be drawn from fixed quarters of the sky.... Difficult questions involving symmetry are solved by means of geometrical theories and methods.

Chapter I, Sec. 4 - De architectura (The Ten Books On Architecture) (~ 15BC) - Book I