Germania Superior

Established along the upper Rhine by Domitian around 83-85 CE and defended by the fortified Limes Germanicus. Alemannic incursions battered the frontier with growing frequency from the mid-3rd century onward, and the province was effectively lost as Roman control west of the Rhine disintegrated in the 5th century. Domitian's campaigns against the Chatti that led to the province's creation were among the few offensive wars of his otherwise defensively-minded reign, and the resulting fortified limes -- a continuous line of walls, ditches, and watchtowers -- represented one of the Roman Empire's most ambitious frontier engineering projects. Legionary fortresses at Mogontiacum (Mainz) and Argentoratum (Strasbourg) anchored the defense and grew into major cities in their own right, garrison towns whose civilian settlements eventually outlasted the military presence that founded them. The province repeatedly changed hands in the chaos of the 3rd-century crisis, with breakaway regimes like the Gallic Empire briefly controlling it independent of Rome. By the time the Rhine frontier finally collapsed in the early 5th century, Alemannic settlement had already been creeping across the limes for generations, and the transition from Roman to Germanic rule there was gradual rather than a single dramatic collapse.

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