Barbarians on the Rhine - Gibbon's Decline and Fall of the Roman Empire Chapter 25 Part 4

The wide waters of the Rhine separated the rich and peaceful provinces of Gaul from the violent barbarians of Germany.  But it was no barrier.  The warlike tribes were only prevented from helping themselves to the property of the empire's inhabitants by the Roman army.  The frontier was tough to defend and during the reign of Constantius had become very porous indeed.  But the stunning victory Julian had scored at the battle of Strasbourg had shocked the Germans.  The glow of invincibility it conferred allowed him to follow up with some effective diplomacy that ensured the peace he had created would last. The watch on the border was as a consequence lighter than usual.  Most of the strain was being taken by some auxiliary units from the tribes of the Batavians and Heruli, who had been settled inside the empire just over the borders as the first line of defence.

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