The counts of Flanders ruled over the county of Flanders from the 9th century. The early rulers from Arnulf I onwards were sometime referred to as margraves (or marquis). This alternate title largely fell out of use by the 12th century.
The counts of Flanders enlarged their estate through a series of diplomatic manoeuvres. The counties of Hainaut, Namur, Bethune, Nevers, Auxerre and Rethel, as well as the duchies of Brabant and Limburg, were acquired via marriage with the respective heiresses. Ironically, the county of Flanders itself, along with all its possessions, suffered the same fate and was annexed by the duchy of Burgundy in 1405.
East Flanders lies east and north-east of the western province, and extends northwards to the neighbourhood of Antwerp.
The count of Flanders thus became a feudatory of the empire as well as of the French crown.
In his time the long contest between Flanders and Holland for the possession of the island of Zeeland was brought to an end by a treaty signed on the 6th of March 1323, by which West Zeeland was assigned to the count of Holland, the rest to the count of Flanders.