The chief incidents in the foreign relations of Henry's reign are his long wars with his shiftless brother Robert, and afterwards with Robert's son, William Clito. He had never forgiven the duke for his attempt to dethrone him by the aid of rebels in 1099; nor did the duke ever forgive him for having so promptly seized England at the moment of the death of William II. The peace which they had made in 1100 did not endure, and a long series of hostilities at last culminated in the battle of Tinchebrai (1106). Here Henry, who had invaded Normandy, completely defeated his brother and took him prisoner. He sent the unfortunate Robert to strict confinement in Cardiff Castle, and kept him there all the days of his life. For the rest of his reign Henry ruled Normandy as well as England, but his dominion in the duchy was very precarious. The baronage hated his strong hand and his strict enforcement of the law. They often rebelled against him, but he never failed to subdue them. When William, surnamed Clito, the son of the imprisoned duke, grew towards man's estate, he had no difficulty in finding partisans in Normandy who would do their best to win him back his father's heritage. Aided by the King of France, who was one of Henry's most consistent enemies, William Clito made several bold attempts to deprive his uncle of Normandy. He did not succeed, but presently he became Count of Flanders, to which he had a claim through his grandmother Matilda, the wife of William the Conqueror. Possessed of this rich country, he grew to be a more serious danger to the English king, but he fell in battle in 1128, while striving with some Flemish rebels, and by his death Henry's position became unassailable. [Sidenote: =Marriage of Princess Matilda to Geoffrey of Anjou.=] The King of England was troubled with many other enemies beside William Clito. Lewis VI. of France, and Fulk, Count of Anjou, were always molesting him. But he gained or lost little by his long and dreary border wars with them. The one noteworthy consequence of this strife was that, to confirm a peace with Count Fulk, the king married his two children to the son and daughter of the lord of Anjou. First, his son William was wedded to the count's daughter (1119), and some years later the Lady Matilda was married to Geoffrey, the count's son and heir (1127). [Sidenote: =Death of Henry's son.--Matilda heiress to the throne.=]