LUGDUNUM, in Ancient Geography, the capital of the Segusiani, in Gallia Celtica, situated on an eminence at the conflux of the Arar and Rhodanus, as the Celtic term dun indicates. It was built by Manutius Plancus, under Augustus, while commanding in that part of Gaul, and thither he led a colony. Lugdunum is now Lyons, capital of the Lyonnais.