The subject of this article, the Prophetic Shield of John III Sobieski (1629–1696), in the Princes Czartoryski Collection in Cracow, is special not only because of its significance as regards the history of Poland (which is discussed in the paper), but it is also interesting in relation to its dual connection to the Edict of Milan, issued over 1700 years ago, in 313 AD. The shield displays an episode from ancient times known as the Battle of the Milvian Bridge, an event of crucial importance for the history of Christianity, which preceded the publication of the edict. Second, in Polish historiography, John III Sobieski, who defeated the Turks at the Battle of Vienna in 1683, and the circumstances of this battle, were likened to Emperor Constantine the Great who promulgated the Edict of Milan and his Battle of the Milvian Bridge. There is another interesting coincidence: the place of origin both of the edict and the shield, decorated using assorted techniques, was Milan.