Brienne

The counts of Brienne held Brienne-le-Chateau in Champagne from the tenth century as vassals of the counts of Champagne. Count Erard II's younger son John ruled Brienne as regent for his nephew and in 1210 married the heiress of the Kingdom of Jerusalem, ruling there as king; he led the Fifth Crusade against Damietta, but after marrying his daughter Isabella II to Emperor Frederick II he lost the kingdom, and in 1229 was elected Latin emperor of Constantinople, ruling there until 1237.

Hugh of Brienne married into the ruling family of Athens, and his son Walter V became duke of Athens in 1308, only to be killed by the Catalan Company at Halmyros in 1311.

Walter VI, count in 1337 and later constable of France, failed to reconquer Athens and fell fighting the English at Poitiers in 1356. When his sister Isabella died in 1360 the county passed to Enghien and then to the Luxembourgs of Saint-Pol; a duchy of Brienne, created in 1587, expired in 1608.