Near the sources of the Orne lived the Gallic tribe of the Sagii or Sagiens, probably a vassal of the Esuvians (or Esuvii for the Romans). Their territory corresponded to that of the former diocese of Sees dismantled with the French Revolution. Under Julius Caesar, the Sagii were integrated into Gallia Lugdunensis and Sees became their capital. From the middle of the 5th century, the diocese was transferred from Exmes to Sees, never to leave.