The Sack of Magdeburg, also called Magdeburg's Wedding () or Magdeburg's Sacrifice (), was the destruction of the Protestant city of Magdeburg on 20 May 1631 by the Imperial Army and the forces of the Catholic League, resulting in the deaths of around 20,000, including both defenders and non-combatants. The event is considered the worst massacre of the Thirty Years' War. Magdeburg, then one of the largest cities in Germany, having well over 25,000 inhabitants in 1630, did not recover its importance until well into the 18th century. Background Archbishopric of Magdeburg The archbishopric of Magdeburg was established as an ecclesiastical principality in 968. In political respect the Erzstift, the archiepiscopal and capitular temporalities, had gained imperial immediacy as prince-archbishopric in 1180. This meant that the archbishop of Magdeburg ruled the town and the lands around it in all matters, worldly and spiritual. Protestant Reformation The citizens of Magdeburg had turned Protestant in 1524 and joined the Schmalkaldic League against the religious policies of the Catholic emperor Charles V in 1531. During the Schmalkaldic War of 1546/47, the Lower Saxon city became a refuge for Protestant scholars, which earned it the epithet Herrgotts Kanzlei (), but also an Imperial ban that lasted until 1562. The citizens refused to acknowledge Emperor Charles's Augsburg Interim and were besieged by Imperial troops under Maurice, Elector of Saxony in 1550/51. Protestant archbishops and Administrators The Roman Catholic archdiocese had de facto turned void since 1557, when the last papally confirmed prince-archbishop, the Lutheran Sigismund of Brandenburg came of age and ascended to the see. Openly Lutheran Christian William of Brandenburg, elected to be archbishop in 1598, was denied recognition by the imperial authorities. Since about 1600, he styled himself Administrator of Magdeburg, as did other Protestant German notables assigned to govern principalities that were de jure property of the Catholic church. Alliance with the Danish king During the Thirty Years' War, Administrator Christian William entered into an alliance with Denmark. In 1626, he led an army from Lower Saxony into the Battle of Dessau Bridge. After Wallenstein won this battle, Christian William fled abroad. In 1629, he fled to the court of King Gustavus Adolphus of Sweden. As a result of these developments, in January 1628, the Magdeburg cathedral chapter deposed Christian William and elected Augustus of Wettin, 13-year-old son of John George I, Elector of Saxony, as Administrator. Augustus did not assume office