August 1217, a French fleet arrived off the coast of Sandwich, bringing Louis soldiers, siege engines and fresh supplies. Hubert de Burgh, Henry's justiciar, set sail to intercept it, resulting in the Battle of Sandwich. De Burgh's fleet scattered the French and captured their flagship, commanded by Eustace the Monk, who was promptly executed. When the news reached Louis, he entered into fresh peace negotiations. Henry, Isabella, Louis, Guala and William came to agreement on the final Treaty of Lambeth, also known as the Treaty of Kingston, on 12 and 13 September. The treaty was similar to the first peace offer, but excluded the rebel clergy, whose lands and appointments remained forfeit. Louis accepted a gift of £6,666 to speed his departure from England, and promised to try to persuade King Philip to return Henry's lands in France. Louis left England as agreed and joined the Albigensian Crusade in the south of France. Restoring royal authority With the end of the civil war, Henry's government faced the task of rebuilding royal authority across large parts of the country. By the end of 1217, many former rebels were routinely ignoring instructions from the centre, and even Henry's loyalist supporters jealously maintained their independent control over royal castles. Illegally constructed fortifications, called adulterine castles, had sprung up across much of the country. The network of county sheriffs had collapsed, and with it the ability to raise taxes and collect royal revenues. The powerful Welsh Prince Llywelyn posed a major threat in Wales and along the Welsh Marches. Despite his success in winning the war, William had far less success in restoring royal power following the peace. In part, this was because he was unable to offer significant patronage, despite the expectations from the loyalist barons that they would be rewarded. William attempted to enforce the traditional rights of the Crown to approve marriages and wardships, but with little success. Nonetheless, he was able to reconstitute the royal bench of judges and reopen the royal exchequer. The government issued the Charter of the Forest, which attempted to reform the royal governance of the forests. The regency and Llywelyn came to agreement on the Treaty of Worcester in 1218, but its generous terms – Llywelyn became effectively Henry's justiciar across Wales – underlined the weakness of the English Crown. Henry's mother was unable to establish a role for herself in the regency government and