After the fall of the Roman Empire, the lands that later became the powerful state of Prussia were inhabited by various Germanic tribes. In the medieval era, the borders of the Prussian territories changed frequently, but Prussia was roughly divided between the regions of Brandenburg-Prussia, East Prussia and West Prussia. After the mid-10th century, Brandenburg and West Prussia were incorporated into the Holy Roman Empire, but East Prussia remained separated from the rest of Germany by Poland.
In the mid-13th century, the Prussian territories were overrun by the Teutonic Knights, who were a military and religious order of German nobles. In Prussia, the knights conquered an extensive domain for themselves along the shores of the Baltic sea. During the 15th century, the knights were driven out of Brandenburg and West Prussia and many of the Prussian lands west of Vistula River were brought under Polish rule. In 1525, Albert of Ansbach and Bayreuth, a member of a branch of the Hohenzollern dynasty and the last grand master of the Teutonic Order, became the Duke of Prussia which was converted to a secular duchy under the crown of Poland. In 1539, in the wake of the Protestant Reformation, Albert adopted Lutheranism and secularized the Teutonic Order and its territories. The German state of Brandenburg-Prussia eventually absorbed the lands and military spirit of these crusading knights.
Brandenburg was located on the northern plain, east of the Elbe River. This region, which abounded in lakes and forests, became the nucleus of the Prussian State in the 15th century. The province of Brandenburg can be seen as the birthplace of modern Germany. Historically known as Brandenburg-Prussia, this region was a "Mark", or border region, that was first named Brandenburg, after the Slavic chieftain seat of Brendaburg. Brandenburg eventually expanded to incorporate the Rhineland, Westphalia, Hannover, parts of Saxony, Pomerania, and Hessen. Before the period of the Great Migration, the Germanic Semnonen tribe lived here before moving south to Swabia. The Slavic tribe of the Heveler, who gave the river Havel its name, then took over this territory until the arrival of the Christian Saxons, who colonized this area east of the Elbe. Albrecht the Bear, in 1184, battled the Slavic tribe of the Wenden as he drove the borders of his region eastwards, naming the march "Brandenburg".
- ^ Swyrich, Archive materials