The Margraviate of Brandenburg, the predecessor to the modern state of Brandenburg, was founded in 931 AD as the Mark of North Saxony, later becoming the Margraviate of Brandenburg.
Here's a more detailed timeline:
931 AD: The territory of Brandenburg, originally called the Mark of North Saxony (Mark Nordsachsen), was established.
1157: The Margraviate of Brandenburg became a major principality of the Holy Roman Empire.
