Rouen is the historical capital city of Normandy, in northwestern France on the River Seine, and currently the capital of the Haute-Normandie (Upper Normandy) region. Once one of the largest and most prosperous cities of medieval Europe, Rouen was the seat of the Exchequer of Normandy in the Middle Ages. It was one of the capitals of the Anglo-Norman dynasties, which ruled both England and large parts of modern France from the 11th century to the 15th century. It was in Rouen where Joan of Arc was burnt in 1431. Rouen was founded by the Gaulish tribe of the Veliocassi, who controlled a large area in the lower Seine valley. They called it Ratumacos; the Romans called it Rotomagus. Roman Rotomagus was 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.