| Arnstein | |
|---|---|
| Country | Saxony-Anhalt, Germany |
| Founded | 12th century |
| Founder | Walter I, Count of Arnstein |
| Final ruler | Luitgard, Countess of Arnstein (main line) Wichmann, Count of Lindow-Ruppin (Lindow-Ruppin line) August Louis, Count of Barby-Mühlingen (Barby-Mühlingen line) |
| Titles | Count |
| Estate | Burg Arnstein |
| Deposition | 1296/1332 (main line) 1524 (Lindow-Ruppin line) 1659 (Barby-Mühlingen line) |
| Cadet branches | Lindow-Ruppin line Barby-Mühlingen line |


The House of Arnstein was an ancient German noble family from the Saxony-Anhalt region. Different lines of the family ruled the County of Arnstein, the County of Ruppin and the County of Barby-Mühlingen.
The Lords (or Counts) of Arnstein descended from the Swabian von Steusslingen family; their first known member was Walter of Steusslingen (died 1056). Walter was the father of Adalbero, who was in turn father of Werner, Bishop of Münster, and also of Walter I, the first lord of Arnstein in Saxony. Their family name was originally spelled Arnstedt, but were later called Arnstein, this last name possibly deriving from the castle they owned, or the land they ruled.
In 1135 they moved to Saxony and built their first known residence: Arnstein Castle, near Aschersleben on the Eastern Harz river. The use of the title Count of Arnstein goes back to the end of the 12th century. In 1289, Walter von Arnstein was burgrave of Freckleben.
The Arnstein dynasty owned land in Mühlingen, in the County of Mansfeld, in the Archbishopric of Magdeburg and in Quedlinburg Abbey (of which they were sub-bailiffs). The Counts of Mühlingen and probably also the Counts of Falkenstein are said to have descended from the family.
In 1196, the three children of Walter III (1150–1196) and his wife Gertrude of Ballenstedt (granddaughter of Albert the Bear) divided their patrimony:
This line was the last to be extinct. After the death of August Louis in 1659, the family's main possessions were inherited by Saxe-Weissenfels and Anhalt-Zerbst.
The coat of arms of the main line of the family shows a silver, gold-armored eagle in black or red.
Lordship of Lindow-Ruppin (1196–1524) |
Lordship of Arnstein (1107–1296) |
Lordship of Barby-Mühlingen (1196–1497) Raised to: County of Barby-Mühlingen (1497–1659) |
| Annexed to Falkenstein | ||
| Annexed to Brandenburg | ||
| Annexed to Saxe-Weissenfels and Anhalt | ||
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(Note: The rulers in the table follow a single counting (as costumary in sources that call Albert X to the count of Barby who died in 1588), in spite of the different parts from where they ruled. This is not, however, a unanimous point of view; some authors choose to individualize the numberings according to the part; that's why, for example, Albert VII of Barby can be also called by some as Albert III).
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