An understudied problem in the history of art, scale—not measurable size, but the sense of relation to size—fundamentally shapes relations between people and material works of art, and thus relations between people and spaces as mediated by visual art, ultimately making possible new configurations of social, political, and environmental relations. During the period 1300-1600, European painting underwent a series of radical reinventions—the emergence of new picture categories, new roles for drawing and new modes of scalable image-replication, new pictorial techniques and supports, as well as new approaches to virtual space—developments that produced continual experimentation with scale, as painters attempted to coordinate new modalities of painting with the viewers and real environments they served. This talk focuses on the development and application of the principle of "life scale," in which depicted figures are depicted to scale with the body of the viewer even as they inhabit pictorial space, a fundamental regrounding that took hold around 1500 and changed European painting forever.