Osterwalde is a medieval shire (Gau) in the Eastphalia

Eastphalia

Eastphalia is a historical region in northern Germany, encompassing the eastern part of the historic Duchy of Saxony, between the Elbe, Leine, Saale and Unstrut rivers. Today, it covers the southeastern part of the state of Lower Saxony and the western part of Saxony-Anhalt.-Etymology:The name...

 region of the Duchy of Saxony

Duchy of Saxony

The medieval Duchy of Saxony was a late Early Middle Ages "Carolingian stem duchy" covering the greater part of Northern Germany. It covered the area of the modern German states of Bremen, Hamburg, Lower Saxony, North Rhine-Westphalia, and Saxony-Anhalt and most of Schleswig-Holstein...

. In present-day terms, it is located in northern Saxony-Anhalt

Saxony-Anhalt

Saxony-Anhalt is a landlocked state of Germany. Its capital is Magdeburg and it is surrounded by the German states of Lower Saxony, Brandenburg, Saxony, and Thuringia.Saxony-Anhalt covers an area of...

. It was bordered by the River Ohre

Ohre

The Ohře is a 316 km long river in Germany and the Czech Republic , left tributary of the Elbe. The basin area of the river has a size of 6,255 km², of which 5,614 km² are in the Czech Republic and 641 km² in Germany...

 to the west and by the River Dumme to the north; its eastern borders are unclear; it possibly reached all the way to the River Elbe

Elbe

The Elbe is one of the major rivers of Central Europe. It rises in the Krkonoše Mountains of the northwestern Czech Republic before traversing much of Bohemia , then Germany and flowing into the North Sea at Cuxhaven, 110 km northwest of Hamburg...

. The most important town was Salzwedel

Salzwedel

Salzwedel of Altmarkkreis Salzwedel, and has a population of approximately 21,500. Salzwedel is located on the German Framework Road.-Geography:...

, other towns were Seebenau

Seebenau

Seebenau is a village and a former municipality in the district Altmarkkreis Salzwedel, in Saxony-Anhalt, Germany. Since 1 January 2010, it is part of the town Salzwedel....

, Tylsen

Tylsen

Tylsen is a village and a former municipality in the district Altmarkkreis Salzwedel, in Saxony-Anhalt, Germany. Since 1 January 2010, it is part of the town Salzwedel....

, and Osterwohle

Osterwohle

Osterwohle is a village and a former municipality in the district Altmarkkreis Salzwedel, in Saxony-Anhalt, Germany. Since 1 January 2010, it is part of the town Salzwedel....

, after which it is probably named. Neighboring shires include Drevani

Drevani

The Drevani were a tribe of Polabian Slavs settling on the Elbe river in the area of the present-day Lüchow-Dannenberg district of Lower Saxony, Germany....

, Choina, Balsamgau

Balsamgau

The Balsamgau was an early medieval Gau in the Eastphalia region of the Duchy of Saxony. It was centered on Stendal and located on the West bank of the River Elbe. Other towns in the Balsamgau include Arneburg, Döbbelin, Elversdorf, Windberge...

, Nordthüringgau

Nordthüringgau

The Nordthüringgau was an early medieval county in the Eastphalia region of the Duchy of Saxony. It was bounded by the River Elbe in the east, by the River Bode in the southwest, the Lappwald in the west, and the Drömling forest in the northwest...

, Derlingau

Derlingau

The Derlingau was an early medieval county of the Duchy of Saxony.-Geography:The Derlingau approximately consisted of the area between the river Oker in the west and the Lappwald forest in the east. It was bordered by : Bardengau, Gau Osterwald, Nordthüringgau, Harzgau, Salzgau, Hastfalagau, Gau...

, and Bardengau

Bardengau

The Bardengau was a medieval county in the Duchy of Saxony. Its main town was Bardowick; other important towns were Lüneburg and Oldenstadt ....

.

By the 12th century, the Gau Osterwalde had become a part of the Margraviate of Brandenburg

Margraviate of Brandenburg

The Margraviate of Brandenburg was a major principality of the Holy Roman Empire from 1157 to 1806. Also known as the March of Brandenburg , it played a pivotal role in the history of Germany and Central Europe....

. Together with the Balsamgau, it formed the westernmost part of Brandenburg, which later came to be known as the Altmark

Altmark

The Altmark is a historic region in Germany, comprising the northern third of Saxony-Anhalt. As the initial territory of the Brandenburg margraves, it is sometimes referred to as the "Cradle of Prussia", as by Otto von Bismarck, a native from Schönhausen near Stendal.- Geography :The Altmark is...

.