ARTHUR III. (1393-1458), earl of Richmond, constable of France, and afterwards duke of Brittany, was the third son of John IV., duke of Brittany, and Joan of Navarre, afterwards wife of Henry IV. of England. His brother, John V., gave him his earl dom of Richmond in England. From 1410 to 1414 he served on the side of the Armagnacs in the civil wars, and afterwards entered the service of Louis the dauphin, whose intimate friend he be came. At Agincourt he was wounded and captured, and he re mained a prisoner in England from 1415 to 142o. Released on parole, he persuaded his brother, the duke of Brittany, to conclude the treaty of Troyes, and was rewarded by Henry V. with the countship of Ivry.
In 1423 Arthur married Margaret of Burgundy, widow of the dauphin Louis, and thus became the brother-in-law of the regent, the duke of Bedford. Offended by Bedford's refusal to give him a high command, he broke with the English, and in March 1425 became constable of France.
He now threw himself with ardour into the French cause, and persuaded his brother, John V. of Brittany, to conclude the treaty of Saumur (Oct. 7 1425) with Charles VII. But he met with a whole series of reverses in the field ; and at court, where his rough and overbearing manners made him disliked, his influence was overshadowed by that of a series of incompetent favourites. The peace concluded between the duke of Brittany and the English in Sept. 1427 led to his expulsion from the court. In June 1429 he joined Joan of Arc at Orleans, and fought in several battles under her banner, till the influence of La Tremoille forced his withdrawal from the army. On March 5 1432, Charles VII. concluded with him and with Brittany the treaty of Rennes; but it was not until June of the following year that La Tremoille was overthrown. Richmond now resumed the war against the English, and re pressed the plundering bands of soldiers and peasants known as routiers or ecorcheurs. On Sept. 20 mainly as a result of his diplomacy, the treaty of Arras was signed between Charles VII. and the duke of Burgundy, to which France owed her salvation.
On April 13 1436, Richmond took Paris from the English ; but it was not till May 1444 that the armistice of Tours gave him lei sure to carry out the reorganization of the army. He now created the compagnies d'ordonnance and endeavoured to organize the militia of the francs archers. This reform had its effect in the struggles that followed. In alliance with his nephew, the duke of Brittany, he reconquered, during Sept. and Oct. 1449, nearly all the Cotentin ; on April 15 145o, he gained over the English the battle of Formigny ; and during the year he recovered for France the whole of Normandy, which for the next six or seven years he defended from English attacks. On the death of his nephew Peter II., Sept. 22 1457, he became duke of Brittany. He reigned little more than a year, dying Dec. 26 1458, and was succeeded by his nephew Francis II., son of his brother Richard, count of 1?tampes.
Duke Arthur was thrice married : (I) to Margaret of Burgundy, duchess of Guienne (d. 1442) ; (2) to Jeanne d'Albret, daughter of Charles II. of Albret (d. ; (3) to Catherine of Luxemburg, daughter of Peter of Luxemburg, count of St. Pol, who survived him. He left no legitimate children.
BIBLIOGRAPHY.—The main source for the life of Duke Arthur III. Bibliography.—The main source for the life of Duke Arthur III. is the chronicle of Guillaume Gruel (c. 1410-74-82). Gruel entered the service of the earl of Richmond about 1425, shared in all his campaigns, and lived with him on intimate terms. The chronicle covers the whole period of the duke's life, but the earlier part, up to 1425, is much less full and important than the later, which is based on Gruel's personal knowledge and observation. In spite of a perhaps exaggerated admiration for his hero, Gruel displays in his work so much good faith, insight and originality that he is accepted as a thoroughly trustworthy authority. It was first published at Paris in 1622. Of the numerous later editions, the best is that of Achille le Vavasseur, Chronique d'Arthur de Richemont (Paris, 1890). See also E. Cosneau, Le Connetable de Richemont (Paris, 1886) ; G. du Fresne de Beaucourt, Histoire de Charles VII. (Paris, 1881, et seq.) .