The Alamanni, or Allemanni or Alemanni, were a Germanic tribe, first mentioned by Dio Cassius, under the year 213. They apparently dwelt in the basin of the Main River, to the south of the Chatti.
According to Asinius Quadratus their name (all men) indicates that they were a conglomeration of various tribes. There can be little doubt, however, that the ancient Hermunduri formed the bulk of the nation. Other groups included the Juthungi, Bucinobantes, Lentienses, and perhaps the Armalausi. From the 4th century onwards we hear also of the Suebi, Suevi or Suabi. The Hermunduri had apparently belonged to the Suebi, but it is likely enough that reinforcements from new Suebic tribes had now moved westward. In later times the names Alamanni and Suebi seem to be synonymous, although some of the Suebi later migrated to Spain and established an independent kingdom there that endured well into the sixth century.
The tribe was continually engaged in conflicts with the Roman Empire. They launched a major invasion of 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 Visigoths. In the early summer, the Emperor Gallienus halted their advance in 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 Strasbourg, in 357. They were defeated by Julian, later Emperor of Rome, and their king Chonodomarius was taken prisoner. On January 2, 366 the Alamanni crossed the frozen Rhine in large numbers, to invade the Roman Empire.
Early in the 5th century the Alamanni appear to have crossed the Rhine river, conquered and then settled what is today Alsace and a large part of Switzerland. Their kingdom (or duchy of Alamannia) lasted until 496, when they were conquered by Clovis I at the Battle of Tolbiac, from which time they formed part of the Frankish dominions. In a strange twist of fate, the word "Frankish" eventually gave its name to the Romance language French, while the Alamanni gave their name to the French word for "German" (Allemand).