Throne of St Peter

Six pointed star engraved in 
13th Century marble throne of St Peter of Castello in Venice, Italy. 

Comes from Antioch. Inscribed with words from the Koran

Probably an ancient Muslim gravestone 

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Source:

http://en.wikipedia.org/wiki/File:Venezia_-_Chiesa_di_San_Pietro_di_Castello_-_Cattedra_di_San_Pietro.JPG