Margraviate of Brandenburg
The Margraviate of Brandenburg, also known as the March of Brandenburg, played a pivotal role in forming the nucleus of what over the course of history became the Kingdom of Prussia and the German Empire. The "Märkischer Adler", or red eagle of the Margraviate of Brandenburg was adopted by Margrave Gero in the 10th century. The bi-color of red over white was used by the Province of Brandenburg in both the Kingdom of Prussia and also in the Free State of Prussia.