[Sidenote: =Defeat of Lewis.--English naval victory.=] The fortune of the civil war soon began to turn in favour of the young king. It was decided by two great battles. Lincoln castle was being besieged by the followers of Lewis, French and English. To relieve it William the Marshal set out with a small army, and, surprising the enemy in the streets of the town, while they were busied in the siege, he inflicted a great defeat upon them. Most of the great English barons of Lewis's party were taken prisoners in the fray. Shortly after a second decisive engagement completely shattered Lewis's hopes. He was expecting great reinforcements from France, which were to be brought to him by a fleet commanded by Eustace the Monk, a cruel pirate captain whom he had hired to serve him because of his naval skill. But Hubert de Burgh, the Justiciar of King Henry, put to sea from Dover with a small squadron of ships raised from the Cinque Ports, and met the French in mid-channel off Sandwich. The English had the better, most of the hostile vessels were captured, and Eustace the Monk was taken and hung for his former piracies. This was the first great naval battle which an English fleet ever won. Deprived of hope of succour from France, and seeing most of his English supporters captives in Pembroke's hands, Prince Lewis resolved to abandon his enterprise and leave England. He proffered terms to Pembroke and de Burgh, who eagerly accepted them. So by the treaty of Lambeth he undertook to depart and give up his claim to the crown, while the Earl Marshal and Justiciar on their part consented to grant an amnesty to all Lewis's partisans, and to restore them to possession of their estates. To facilitate Lewis's quick retreat he was given a sum of 10,000 marks (September 17, 1217). [Sidenote: =Hubert de Burgh Justiciar.=]