Arimannia (from Lombard ari-mann, "man of the army", that is "free man active in the army"; akin German "heer-mann") was - during the Lombard domination in Italy - a group of warriors directly subjected to the King. The aim of an Arimannia was the defence of an important strategic point.
Although documented only from the 8th century CE, the Arimannia is believed to have existed since the Lombard invasion of Italy.
References
Arimannia Wikipedia(Text) CC BY-SA