The Alamanni were continually engaged in conflicts with the Roman Empire. They launched a major invasion of Gaul and northern Italy in 268, when the Romans were forced to denude much of their German frontier of troops in response to a massive invasion of the Goths from the east. Their raids throughout the three parts of Gaul were traumatic: Gregory of Tours (died ca 594) mentions their destructive force at the time of Valerian and Gallienus (253–260), when the Alemanni assembled under their "king", whom he calls Chrocus, who "by the advice, it is said, of his wicked mother, and overran the whole of the Gauls, and destroyed from their foundations all the temples which had been built in ancient times. And coming to Clermont he set on fire, overthrew and destroyed that shrine which they call Vasso Galatae in the Gallic tongue," martyring many Christians (Historia Francorum Book I.32–34). Thus 6th century Gallo-Romans of Gregory's class, surrounded by the ruins of Roman temples and public buildings, attributed the destruction they saw to the plundering raids of the Alemanni.
In the early summer of 268, the Emperor Gallienus halted their advance into Italy, but then had to deal with the Goths. When the Gothic campaign ended in Roman victory at the Battle of Naissus in September, Gallienus' successor Claudius II Gothicus turned north to deal with the Alamanni, who were swarming over all Italy north of the Po River.
After efforts to secure a peaceful withdrawal failed, Claudius forced the Alamanni to battle at the Battle of Lake Benacus in November. The Alamanni were routed, forced back into Germany, and did not threaten Roman territory for many years afterwards.
Their most famous battle against Rome took place in Argentoratum (Strasbourg), in 357, where they were defeated by Julian, later Emperor of Rome, and their king Chnodomarius was taken prisoner to Rome.
On January 2 366 the Alamanni yet again crossed the frozen Rhine in large numbers, to invade the Gallic provinces, this time being defeated by Valentinian (see Battle of Solicinium). In the great mixed invasion of 406, the Alamanni appear to have crossed the Rhine river a final time, conquering and then settling what is today Alsace and a large part of the Swiss Plateau. The crossing is described in Wallace Breem's historical novel "Eagle in the Snow." Fredegar's Chronicle gives the account. At Alba Augusta (Alba-la-Romaine) the devastation was so complete, that the Christian bishop retired to Viviers, but in Gregory's account at Mende in Lozère, also deep in the heart of Gaul, bishop Privatus was forced to sacrifice to idols in the very cave where he was later venerated. It is thought this detail may be a generic literary ploy to epitomize the horrors of barbarian violence.
Alamanni - Wikipedia, the free encyclopedia 