The most powerful of these were the Franks (who, at the time, resided between the Rhine and the Somme) and they converted to Catholic Christianity, during the reign of King Clovis I around 500 AD. Most of the region thus fell under the Frankish Kingdom and then the Carolingian Empire until the end of the 9th century. From the center of the Diocese of Tongeren-Maastricht-Liège, successively the cities of Tongeren, Maastricht and Liège, this part of the Low Countries was probably Christianized. According to tradition, the first Bishop of Maastricht, Servatius, was buried in this city in 384, though only from Bishop Domitianus (ca. 535) is it established that he resided in Maastricht.