The Great Prussian Uprising among the old Prussians begins against the Teutonic Knights.

The Prussian uprisings were two major and three smaller uprisings by the Old Prussians, one of the Baltic tribes, against the Teutonic Knights that took place in the 13th century during the Prussian Crusade. The crusading military order, supported by the Popes and Christian Europe, sought to conquer and convert the pagan Prussians. In the first ten years of the crusade, five of the seven major Prussian clans fell under the control of the less numerous Teutonic Knights. However, the Prussians rose against their conquerors on five occasions.

September 20 is the 263rd day of the year in the Gregorian calendar; 102 days remain until the end of the year.