In 1347 Charles IV, the Roman and Bohemian king, awarded Prague’s Archbishop the right to coronate the king of Bohemia.
The charter is a Golden Bull, also known as Chrysobulls. These were imperial decrees issued in the Byzantine Empire and later in the Middle Ages and Renaissance by the Holy Roman Emperor.
The Golden Bulls of Charles are majestic; filled with wax, they contain the most authentic gold, with a small ratio of silver, copper, and zinc. In this case, the back portrays a sketch of St. Peter’s Basilica, a symbolic picture of the eternal city of Rome.
See: https://www.archivesportaleurope.net/featured-document/-/fed/pk/94804#sthash.GR44XYI6.dpbs
Archives Portal Europe Blog 