"Black Room" in a Villa at Boscotrecase believed to have been owned by Agrippa Postumo
Image copyright © : The Metropolitan Museum of Art, New York http://www.metmuseum.org/toah/hd/bsco/ho_20.192.1-.3.htm (October 2006)

 

Although both wall-paintings are referred to as Third Style the image on the right makes no use of a secondary spatial plane, whilst the above uses window-like openings that are also an identifying feature of the Fourth Style. It was in response to iconographic problems such as this one that the concept of transitional phases within styles evolved, largely undertaken by German and Dutch scholars.