“Frames evolved from the borders which appeared 3-4,000 years ago on vase and tomb paintings, and later on mosaics, enclosing narrative scenes and decorative panels. Early Christian art adapted these to the carved edgings of ivory book covers and diptychs, and finally of altarpieces. By this time the function of the frame had changed: not merely a decorative boundary, it protected and emphasized the work it held, and might have a strongly symbolic aspect.” (Thanks Coudal Partners!)