How did Augustus divide Roman Gaul into provinces?

The emperor Augustus organized Transalpine Gaul into four distinct administrative provinces. This division separated the region into a senatorial province and three imperial provinces:123

• Narbonensis: Located between the Mediterranean and the other three provinces, this was a senatorial province governed by a proconsul appointed by the Senate.32
• The Three Gauls (Tres Galliae): These were imperial provinces, each ruled by an imperial legate of praetorian standing. They included:32
  • Aquitania: Bordered by the Pyrenees and the Bay of Biscay.3
  • Lugdunensis: Centered on its capital, Lugdunum (Lyon), and extending northwest toward Brittany.3
  • Belgica: Situated in the north, with chief towns at Trier and Reims.3

While the senatorial province of Narbonensis was heavily Romanized and settled with colonies of retired soldiers, the three imperial provinces retained their traditional civitates (tribal nations) as the primary administrative units.4