Walter V of Brienne (; – 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 in the battlefield and the Catalans occupied the Duchy of Athens. Early life Born around 1275, Walter was the only son of Hugh of Brienne and Isabella de la Roche. Hugh held important fiefs both in France (the county of Brienne), and in southern Italy (the counties of Lecce and Conversano). He had also claimed Cyprus, but the Cypriots elected his cousin Hugh of Antioch-Lusignan as king. Isabella de la Rochethe younger daughter of Duke Guy I of Athensbrought Peloponnesian estates into the marriage. She died in 1279. Historian Guy Perry describes Walter as a "veritable child" of the War of the Sicilian Vespers (1282–1302). His father, who was a military commander of King Charles II of Naples, fell into captivity in the Battle of the Counts on 23 June 1287. Hugh was released