An early archbishop of this city was called "Apostle of the Slavs" for converting Polabian Slavs.  
An early archbishop of this city was called "Apostle of the Slavs" for converting Polabian Slavs.  An ecclesiastical history called "[this city's] Centuries," written by Matthias Flacius, covers 13 centuries up to the year 1298, and accuses the pope of being the Anti-Christ. A charter written in this city in 1108, attributed to Archbishop Adelgot called for a Christian war of conversion, and led Boleslaw III to conquer Pomerania. A set of rights named for this city, developed under Otto the Great, became the basis for the town laws of the Holy Roman Empire. This city's namesake "quarter" became a synonym for lack of mercy after almost all of its residents were slaughtered, except the few that took refuge in this city's cathedral, the oldest German Gothic church. That Imperial siege of this city was led by Pappenheim and Count Tilly in 1631. For 10 points, name this German city on the Elbe which was sacked during the Thirty Years' War.
An early archbishop of this city was called "Apostle of the Slavs" for converting Polabian Slavs.  
Magdeburg [or Meideborg]