On the arrival of the latter in England he was constituted sheriff of Gloucestershire and of Sussex, and was shortly afterwards sent into Normandy at the head of a large body of forces. He commanded in the famous battle fought A. D. 1202 before the fortress of Mirabel, in which the unfortunate prince Arthur and his lovely sister Eleanor, "the pearl of Brittany," were taken prisoners, together with the earl of March, most of the nobility of Poictou and Anjou, and two hundred French knights, who were ignominiously put into fetters, and sent away in carts to Normandy. This battle was followed, as is well known, by the mysterious death of prince Arthur, who is said to have been murdered by king John himself, whilst the beautiful Eleanor, nicknamed _La Bret_, who, after the death of her brother, was the next heiress to the crown of England, was confined in close custody in Bristol Castle, where she remained a prisoner for life. At the head of four thousand infantry and three thousand cavalry, the earl Marshall attempted to relieve the fortress of Chateau Gaillard, which was besieged by Philip king of France, but failed in consequence of the non-arrival of seventy flat-bottomed vessels, whose progress up the river Seine had been retarded by a strong contrary wind.[508] For his fidelity and services to the crown he was rewarded with numerous manors, lands, and castles, both in England and in Normandy, with the whole province of Leinster in Ireland, and he was made governor of the castles of Caermerden, Cardigan, and Coher. In the year 1204 he was sent ambassador to Paris, and on his return he continued to be the constant and faithful attendant of the English monarch. He was one of the witnesses to the surrender by king John at Temple Ewell of his crown and kingdom to the pope,[509] and when the barons' war broke out he was the constant mediator and negotiator between the king and his rebellious subjects, enjoying the confidence and respect of both parties. When the armed barons came to the Temple, where king John resided, to demand the liberties and laws of king Edward, he became surety for the performance of the king's promise to satisfy their demands. He was afterwards deputed to inquire what these laws and liberties were, and after having received at Stamford the written demands of the barons, he urged the king to satisfy them. Failing in this, he returned to Stamford to explain the king's denial, and the barons' war then broke out. He afterwards accompanied king John to the Tower, and when the barons entered London he was sent to announce the submission of the king to their desires. Shortly afterwards he attended king John to Runnymede, in company with Brother Americ, the Master of the Temple, and at the earnest request of these two exalted personages, king John was at last induced to sign MAGNA CHARTA.[510]