Istvaeones

The Istvaeones (also spelled Istaevones) were a Germanic group of tribes living near the banks of the Rhine during the Roman Empire which reportedly shared a common culture and origin. The Istaevones were contrasted to neighbouring groups, the Ingaevones on the North Sea coast, and the Herminones, living inland of these groups.

A proposed distribution of the primary Germanic dialect groups in Europe in around AD 1. The depiction of Jutland as a West Germanic area is typical within German scientific tradition.
  North Sea Germanic, or Ingvaeonic
  Weser-Rhine Germanic, or Istvaeonic
  Elbe Germanic, or Irminonic

In linguistics, the term "Istvaeonic languages" is also sometimes used in discussions about the grouping of the northwestern West Germanic languages, consisting of Frankish and its descendants (principally Old Dutch) as well as several closely related historical dialects.[1] Whether or not the Istvaeones spoke a Germanic language according to modern definitions, the theory proposes that their language indirectly influenced later Germanic languages in the area as a substrate.