Battle of Lützen
At this time, the Catholic Holy Roman Empire used the Gregorian calendar, but Protestant Sweden still used the Julian calendar. Hence the Battle of Lützen occurred on 16 November for the Catholics but on 6 November for the Swedes. In Sweden, the death of Gustavus Adolphus has a long tradition of being commemorated on 6 November, Gustavus Adolphus Day, despite the country's adoption of the Gregorian calendar in the 18th century.