FAST COMPANY -- The medium can be traced back to Mexican painter Diego Rivera, who revitalized the mural in the early 20th century. As Robert W. Cherny, professor emeritus of History at San Francisco State University, explains, Rivera learned mural-making by studying art of the old masters from the Renaissance in Europe. They made murals by more than just painting on a wall. They used a technique called fresco that requires a layer of wet plaster on a surface, which you paint while the plaster dries. The technique melts the image into the surface of a building, turning it into a piece of the urban landscape.