From the beginning of English historical writing authors have shown interest in the meaning of place-names. The Venerable Bede sometimes renders Old English names correctly into Latin (as Insula uituli marini for Selsey), but in many instances he displays the tendency shared by many modern philologists to rely overmuch on eponymous persons, as in his conjecture of a chieftain called Hrof to explain Hrofesceaster (modern Rochester). This tendency is even more marked in the men who compiled the Anglo-Saxon Chronicle in the late 9th century. They inferred the existence of chieftains such as Port from place-names like Portsmouth which do not contain personal names, and assigned to them roles in the conquest of southern Britain. In early times in Ireland, place-name lore, or dinnseanchas, was a recognized branch of learning, but it was related to literature rather than to history, and it consisted of highly fanciful etymologies. In early medieval society there was probably so great a gap between the preoccupations of learned men and those of the peasant farmers among whom place-names arose that the conjectures of the former were bound to be wide of the mark.
From The Oxford Companion to Local and Family History in Oxford Reference.