Henry II wanted to secure the southern borders of Aquitaine and decided to betroth his youngest son to Alais, the daughter and heiress of Humbert III of Savoy. As part of this agreement John was promised the future inheritance of Savoy, Piedmont, Maurienne, and the other possessions of Count Humbert. For his part in the potential marriage alliance, Henry II transferred the castles of Chinon, Loudun and Mirebeau into John's name; as John was only five years old his father would continue to control them for practical purposes. Henry the Young King was unimpressed by this; although he had yet to be granted control of any castles in his new kingdom, these were effectively his future property and had been given away without consultation. Alais made the trip over the Alps and joined Henry II's court, but she died before marrying John, which left the prince once again without an inheritance.

Henry II wanted to secure the southern borders of what?