The first documented mention of Prienai is in 1502 when the Grand Duke of Lithuania Alexander gave the land of Prienai to the noble Mykolas Glinskis, who, following his exile from the Grand Duchy of Lithuania, became the tutor of his nephew Ivan the Terrible. In 1609, the city was granted the Magdeburg rights, though they were greatly expanded in 1791 by the Grand Duke of Lithuania Stanislaw II Augustus. The city's arms showing St. George killing the dragon was granted in the same year. St. George was one of the patron saints of the Grand Duchy of Lithuania.