Dux et princeps Francorum

The title Duke [and Prince] of the Franks (dux [et princeps] Francorum) has been used for three different offices, always with "duke" implying military command and "prince", on those occasions when it was used either with or in preference to "duke", implying something approaching sovereign or regalian rights. The term "Franks" may refer to an ethnic group or the inhabitants of a territory called "Francia", named after the original Franks. The first office was that of the mayors of the palace of the Merovingian kings of the Franks, whose powers increased as those of the kings declined. The second was that of the second-in-command to the early kings of France, the last incumbent of which succeeded to the throne in 987. This title was sometimes rendered Duke of France (dux Franciae). The third instance was that of the rulers of the Frankish-inhabited lands of Germany, the so-called "tribal" duchy of Franconia.

Up until the time after Dagobert I, the title princeps (prince) had royal connotations. The first time it was used to describe the mayors of the palace of Neustria was in mid-7th-century saints' lives. The Vita Eligii refers to unspecified principes of the palatium of Neustria, and the Vita Baldechildis and Passio Leudegarii describe the mayors Erchinoald and Ebroin as princes.Pippin II first used the title princeps after his victory at the Battle of Tertry in 687. Both the Liber historiae Francorum and the Vita Dagoberti tertii refer to him by this title, but the continuation of the Chronicle of Fredegar uses only the title "duke". The historian Bede refers to Pippin II as dux Francorum, but the ninth-century Anglo-Saxon translator of Bede uses the term Froncna cyning (king of the Franks). The continuator of Fredegar refers to Ragamfred as a prince, but he only calls his rival, Pippin's son Charles Martel, a prince after his defeat of Ragamfred in 718. The princely title was used continuously from this point on for Charles and his descendants, the Carolingians, both in narrative and charter sources.

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