Gallia Lugdunensis
Rouen was founded by the Gaulish tribe of the Veliocasses, who controlled a large area in the lower Seine valley. They called it "Ratumacos"; the Romans called it "Rotomagus". It was considered the second city of Gallia Lugdunensis after Lugdunum (Lyon) itself. Under the reorganization of Diocletian, Rouen was the chief city of the divided province Gallia Lugdunensis II and reached the apogee of its Roman development, with an amphitheatre and "thermae" of which foundations remain. In the 5th century, it became the seat of a bishopric and later a capital of Merovingian Neustria.