Their family name was originally spelled Arnstedt, but were later called Arnstein,[3][4] 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 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).

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.

The coat of arms of the main line of the family shows a silver, gold-armored eagle in black or red.