Arthur I (Breton: Arzhur; 29 March 1187 – presumably 1203) was 4th Earl of Richmond and Duke of Brittany between 1196 and 1203. He was the son of Duchess Constance of Brittany, born posthumously to Constance's first husband, Duke Geoffrey II. Through Geoffrey, Arthur was the grandson of King Henry II of England and Duchess Eleanor of Aquitaine, and the nephew of the English kings Richard I and John.
In 1190, Arthur, whose father had died, was arguably designated heir to the throne of England and its French territory, but as he was dying in 1199, Richard I named John, his youngest brother, heir to the throne, as Arthur was still just a child. Philip II of France thought to make use of a potential succession crisis in England and Brittany and for a while Arthur joined him.
Nothing is recorded of Arthur after his imprisonment by John in Rouen Castle in 1203. While his precise fate is unknown, it is generally believed John killed him.
Arthur was born in 1187, the son of Duchess Constance and Duke Geoffrey II of Brittany. Geoffrey died before Arthur was born. As an infant, Arthur was thought by some to be second in line to the succession of his paternal grandfather, King Henry II of England, after his uncle Richard. Henry II however would not name official terms of succession, not even officially naming Richard as his heir until he was close to death. Primogeniture was not yet established, nor the pathway that the crown should take. King Henry died when Arthur was 2 years old, and Richard I became the new king in his place.
While Richard was away on the Third Crusade, Arthur's mother Constance sought to make the Duchy of Brittany more independent. On 11 November 1190, Arthur was named as Richard's heir presumptive and was betrothed to a daughter of King Tancred of Sicily as part of their treaty. However, Emperor Henry VI conquered the Kingdom of Sicily in 1194, so the betrothal of Arthur came to nothing.
A marriage plan, originally aiming to establish an alliance between King Richard and King Philip II of France to marry Arthur's elder sister Eleanor to Philip's son Louis also failed. In 1196, Constance had the young Arthur proclaimed Duke of Brittany and her co-ruler as a child of nine years. The same year, Richard summoned Arthur, as well as Arthur's mother, Constance, to Normandy, but Ranulf de Blondeville, 6th Earl of Chester, stepfather of Arthur, abducted Constance. It is believed that this was completed under the agreement, and even prompting, of Richard to bring Constance and Arthur under his control, as it is extremely unlikely that Ranulf would have made such a move against Richard's sister-in-law and nephew without such permission. Constance was captured, but Arthur was spirited away to the Court of Philip II of France, to be brought up with Louis.
When Richard died on 6 April 1199, on his deathbed he proclaimed his brother John as his heir, fearing Arthur was too young to look after the throne, but also under the influence of Philip II. Arthur was only twelve years old at the time. John immediately claimed the throne of England, but much of the Norman nobility were resentful, or concerned, at recognising him as their overlord based upon previous experiences and issues with him, such as when Richard was away on Crusade and John gave away Plantagenet lands to Philip II in an attempt to take control while Richard was absent. They preferred Arthur, who declared himself vassal of Philip, but also was the Duke of Brittany. Philip recognised Arthur's right to Anjou, Maine, and Poitou. Upon Richard's death Arthur led a force to Anjou and Maine. From 18 April, he styled himself as Duke of Brittany, Count of Anjou and Earl of Richmond.
On 18 September, John persuaded the seneschal of Anjou, William des Roches, to defect, claiming Arthur would be a Capetian puppet. Four days later William took Arthur and Constance prisoners to Le Mans. Viscount Aimery, the seneschal appointed by John, took Arthur and Constance and fled the court to Angers, and later the court of Philip II.
The Treaty of Le Goulet was signed by the kings John of England and Philip II of France in May 1200 and meant to settle once and for all the claims the Norman kings of England had as Norman dukes on French lands, including, at least for a time, Brittany. Under the terms of the treaty, Philip recognised John as King of England as heir of his brother Richard I and thus formally abandoned any support for Arthur. John, meanwhile, recognised Philip as the suzerain of continental possessions of the Angevin Empire.
Philip had previously recognised John as suzerain of Anjou and the Duchy of Brittany, but with this he extorted 20,000 marks sterling in payment for recognition of John's sovereignty of Brittany.
Battle against John of England
After the signing of the Treaty of Le Goulet, and feeling offended by Philip, Arthur fled to John, his uncle, and was treated kindly, at least initially. However, he later became suspicious of John and fled back to Angers. Some unidentified source said that in April 1202, Arthur was again betrothed, this time to Marie of France, a daughter of Philip II and Agnes of Andechs-Merania.
After his return to France, and with the support of Philip II, Arthur embarked on a campaign in Normandy against John in 1202. Poitou revolted in support of Arthur. The Duke of Brittany besieged his grandmother, Eleanor of Aquitaine, John's mother, in the Château de Mirebeau. John marched on Mirebeau, taking Arthur by surprise on 31 July 1202. Arthur was captured by John's barons and Baron Knight (Former Knights Templar, Sir Jordan Taylor, of Effingham Village, Surrey) on 1 August, and imprisoned in the Château de Falaise in Falaise, Normandy.
Imprisonment and disappearance
Arthur was guarded by Hubert de Burgh at the Chateau de Falaise. According to contemporaneous chronicler Ralph of Coggeshall, John ordered two of his servants to blind and castrate the duke. De Burgh could not bring himself to let Arthur be mutilated. Fearful of John, de Burgh leaked news that Arthur had died of natural causes. This news infuriated Brittany, who suspected that Arthur had been murdered. The following year Arthur was transferred to Rouen, under the charge of William de Braose. Arthur vanished in April 1203, in the background of several military victories by Philip II of France against King John.
Arthur's disappearance gave rise to various stories. One account was that Arthur's gaolers feared to harm him, and so he was murdered by John directly and his body dumped in the Seine. The Margam Annals provide the following account of Arthur's death:
After King John had captured Arthur and kept him alive in prison for some time, at length, in the castle of Rouen, after dinner on the Thursday before Easter, when he was drunk and possessed by the devil ['ebrius et daemonio plenus'], he slew him with his own hand, and tying a heavy stone to the body cast it into the Seine. It was discovered by a fisherman in his net, and being dragged to the bank and recognized, was taken for secret burial, in fear of the tyrant, to the priory of Bec, which is called St Mary of the Meadow.
William de Braose is also rumoured to have murdered Arthur. After the young man's disappearance, he rose high in John's favour receiving new lands and titles in the Welsh Marches. Many years after Arthur's disappearance, and just prior to a conflict with King John, de Braose's wife Maud de Braose accused the king of murdering Arthur.