Shaped canvases are paintings that depart from the normal flat, rectangular configuration. Canvases may be shaped by altering their outline, while retaining their flatness. An ancient, traditional example is the "tondo", a painting on a round panel or canvas: Raphael, as well as some other Renaissance painters, sometimes chose this format for madonna paintings. Alternatively, canvases may be altered by losing their flatness and assuming a three-dimensional surface. Or, they can do both. That is, they can assume shapes other than rectangles, and also have surface features that are three-dimensional. Arguably, changing the surface configuration of the painting transforms it into a sculpture. But shaped canvases are generally considered paintings.