As Constable of France, Arthur fought alongside Joan of Arc during her victory at the Battle of Patay on 18 June 1429. He joined his brother John in the siege of Pouancé in 1432, where he notably but reluctantly fought alongside English captains, as the Duke of Brittany was allied with the English at the time. Around this time he received an offer from the Duke of Bedford (who hoped to exploit the conflict between Richemont and la Trémoille), which included Trémoille's lands in Poitou in return for him switching sides. Poitou was not in English hands; still he found more prudent to seize those lands through less strenuous means. On the 5th of March 1432 Charles VII concluded with him and with Brittany the treaty of Rennes; but it was not until June of the following year that Trémoille was overthrown. Arthur now resumed the war against the English, and at the same time took vigorous measures against the plundering bands of soldiers and peasants known as "routiers" or "écorcheurs".