Historical information becomes clearer by early Carolingian time, when a Frisian kingdom united the whole area from present-day West Frisia (the Dutch provinces of Friesland and Groningen and part of North Holland) throughout East Frisia up to the river Weser. It was ruled by kings like the famous Radbod whose known names were still mentioned in folk tales until recent times. Frisia was a short-lived kingdom, and it was crushed by Pippin of Herstal in 689. East Frisia then became part of the Frankish Empire. Charles the Great then divided East Frisia into two counties. At this time, Christianization by the missionaries Liudger and Willehad started; one part of East Frisia became a part of the diocese of Bremen, the other the diocese of Münster.