Map of the Rhine by T.A. Dodge

Map of the Rhine river which acted as the boundary between Gaul and Germany (Caesar's Gallic War 4.16). From Theodore Ayrault Dodge, Caesar: A History of the Art of War Among the Romans Down to the End of the Roman Empire, with a Detailed Account of the Campaigns of Caius Julius Caesar (Boston: Houghton Mifflin, 1892), p. 158.