Ammianus Marcellinus Res Gestae 15.4.1

[1] The affair thus ended, war was declared on the . . . ¹ and Lentienses, ² tribes of the Alamanni, who often made extensive inroads through the Roman frontier defences. On that expedition the emperor himself set out and came to Raetia and the Campi Canini; ³ and after long and careful deliberation it seemed both honorable and expedient that, while he waited there with a part of the soldiers, Arbetio, commander of the cavalry, with the stronger part of the army should march on, skirting the shores of Lake Brigantia, ⁴ in order to engage at once with the savages. Here I will describe the appearance of this place as briefly as my project allows.