La Rogue-Gagea on the Dordogne River, France
The Dordogne (Occitan: Dordonha) is a river in south-central and southwest France. Contrary to appearances, the name of the Dordogne is not a recent word resulting from the names of the Dore and the Dogne. It comes from an ancient Durānius, dérived from a Pre-Celtic root dur-, dor- (as the Durance).The river rises on the flanks of Puy de Sancy (1 885 m) in the mountains of Auvergne, from the confluence of two small torrents above the town of Mont-Dore: the Dore and the Dogne. It flows generally west about 500 km through the Limousin and Périgord regions before flowing into the Gironde, its common estuary with the Garonne, at the "Ambès beak", in the north of the city of Bordeaux.
The medieval forms adopted a redoubled suffix -ononia: Dorononia fluvius (sixth century), Dornonia (eighth century) that evolves in Dordonia (ninth century) by a phenomenon of dissimilation, giving the impression of an etymology *Dore-Dogne.