Carlo Pellicani (after Carlo Buzzi), The Heavenly Throne
West façade, Cathedral of the Nativity of Mary
The throne in this relief has at least three symbolic referents. First, it is pictured as being empty, like the "mercy seat" in the Jerusalem Temple (see Exodus 25:17-22 and I Chronicles 28:11). Secondly, it is flanked by the "four living creatures" of Revelation 4:6-7 and thus relates the historical throne to that which is to come in the "new Jerusalem" (Revelation 21:1-2). The walled city in the background can point in both these directions, as indeed can the four creatures, which Christian exegetes took to refer to the four Evangelists.
Thirdly, there seems to be an allusion to the cathedral's namesake, the Virgin Mary, the "Throne of Wisdom": On the back of the throne is a low relief of a vase of flowers such as one finds on countless images of the Annunciation.
It is very unusual for the third living creature to be pictured as a woman with breasts, especially as the text says it had "the face, as it were, of a man" (4:7, in the Vulgate faciem quasi hominis).
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Read more about images of the evangelists as a group.
Read more about about Mary as "Throne of Wisdom."
Photographed at the site by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.