メルセン条約
Meanwhile, Boso of Provence, a noble of Carolingian descent, proclaimed himself king of Provence (see: Lower Burgundy). Moreover, the Vikings resumed their attacks. To deal with these threats, the Carolingian kings decided to put aside their differences so as to deal with the threats together. They met at Ribemont, in present-day Aisne. In return for Louis the Younger's neutrality, the kings of France confirmed Louis' possession of the parts of Lotharingia that had been given to him since the Treaty of Meerssen. This left them free to deal with Boso.