Walter V, Count of Brienne

Walter V
Walter's seal, appended to his last testament
Duke of Athens
Reign	1308 – 1311
Predecessor	Guy II
Successor	Manfred
Born	c. 1275
Died	15 March 1311 (aged 35–36) Battle of Halmyros, Duchy of Athens
Spouse	Joanna of Châtillon
Issue	Walter VI of Brienne Isabella
House	Brienne
Father	Hugh of Brienne
Mother	Isabella de la Roche
Religion	Roman Catholic

Walter V of Brienne (French: Gautier; c. 1275 – 15 March 1311) was Duke of Athens from 1308 until his death. Being the only son of Hugh of Brienne and Isabella de la Roche, Walter was the heir to large estates in France, the Kingdom of Naples, and the Peloponnese. He was held in custody in the Sicilian castle of Augusta between 1287 and 1296 or 1297 to secure the payment of his father's ransom to the Aragonese admiral Roger of Lauria. When his father died fighting against Lauria in 1296, Walter inherited the County of Brienne in France, and the counties of Lecce and Conversano in southern Italy. He was released, but he was captured during a Neapolitan invasion of Sicily in 1299. His second captivity lasted until the Treaty of Caltabellotta in 1302.

Walter settled in France and married Joanna of Châtillon. After his cousin Duke Guy II of Athens died childless in 1308, Walter laid claim to the Duchy of Athens. Their cousin Eschiva of Ibelin also claimed the duchy, but the High Court of Achaea passed a judgement in Walter's favor. Walter came to Athens in 1309. John II Doukas, the Greek lord of Thessaly, made an alliance against him with the Byzantine Empire and the Despotate of Epirus. Walter hired the Catalan Company, a group of mercenaries, to invade Thessaly. The Catalans defeated John, but Walter refused to pay their wages. After the Catalans rose up in open rebellion, Walter assembled a large army from Frankish Greece, but the Catalans inflicted a crushing defeat on the Franks in the Battle of Halmyros. Walter died on the battlefield and the Catalans occupied the Duchy of Athens.