Battle of Bouvines

In the Battle of Bouvines, July, 1214, Philip Augustus of France defeated Otto IV of Germany and the count of Flanders so decisively that Otto was deposed and replaced by Frederick II Hohenstaufen. Philip was himself able to take undisputed control of the territories of Anjou, Brittany, Maine, Normandy, and the Touraine, which he had recently seized from Otto's ally John I of England.

Bouvines is between Lille and Tournai, and in the 13th century was in the County of Flanders and is part of modern Belgium.

Further reading:

Georges Duby, The Legend of Bouvines (1990). A careful study of the historiography of a single event, Duby examines how the Battle of Bouvines has been used and abused in French history.