Even though a regularized system of perspective had not yet been developed, early fourteenth-century Italian artists Pietro Lorenzetti searched for ways to suggest that a painting was a window onto another visible world in which the artist tried to control the perception of forms in space. These panels, which formed the center of a large altarpiece (whose other elements are now dispersed and lost), represent one of Lorenzetti's most successful and carefully calculated illusions of three-dimensionality. The angels in the spandrels rest their folded arms on the frame as if to mark a limit between their world and that of the viewer, while the Virgin and Child twist in opposite directions to draw attention to their positions within the painting's space. Subtle details, such as the fringe from the Virgin's mantle that falls over the front step, add to our awarenenss of depth. The kneeling figure is a monk or friar. As was then traditional, his diminutive dimensions identify him as a donor and underscore his devotion to the holy figures. It was probably he who commissioned the altarpiece for his church. Carl Brandon Strehlke, from Philadelphia Museum of Art: Handbook of the Collections (1995), p. 162.