1175 Richard was dispatched to Aquitaine to punish the barons who had fought for him. The historian John Gillingham notes that the chronicle of Roger of Howden is the main source for Richard's activities in this period. According to the chronicle, most of the castles belonging to rebels were to be returned to the state they were in 15 days before the outbreak of war, while others were to be razed. Given that by this time it was common for castles to be built in stone, and that many barons had expanded or refortified their castles, this was not an easy task. Roger of Howden records the two-month siege of Castillon-sur-Agen; while the castle was "notoriously strong", Richard's siege engines battered the defenders into submission. On this campaign, Richard acquired the name "the Lion" or "the Lionheart" due to his noble, brave and fierce leadership. He is referred to as "this our lion" () as early as 1187 in the of , while the byname "lionheart" () is first recorded in Ambroise's in the context of the Accon campaign of 1191. Henry seemed unwilling to entrust any of his sons with resources that could be used against him. It was suspected that Henry had appropriated Alys, Richard's betrothed, the daughter of Louis VII of France by his second wife, as his mistress. This made a marriage between Richard and Alys technically impossible in the eyes of the Church, but Henry prevaricated: he regarded Alys's dowry, Vexin in the Île-de-France, as valuable. Richard was discouraged from renouncing Alys because she was the sister of King Philip II of France, a close ally. After his failure to overthrow his father, Richard concentrated on putting down internal revolts by the nobles of Aquitaine, especially in the territory of Gascony. The increasing cruelty of his rule led to a major revolt there in 1179. Hoping to dethrone Richard, the rebels sought the help of his brothers Henry and Geoffrey. The turning point came in the Charente Valley in the spring of 1179. The well-defended fortress of Taillebourg seemed impregnable. The castle was surrounded by a cliff on three sides and a town on the fourth side with a three-layer wall. Richard first destroyed and looted the farms and lands surrounding the fortress, leaving its defenders no reinforcements or lines of retreat. The garrison sallied out of the castle and attacked Richard; he was able