What is "ahrgau"

The Ahrgau (also Argau) was a mediaeval Frankish gau county, that lay either side of the River Ahr in the north of the present-day German state of Rhineland-Palatinate, but also reached the gates of Bonn (the Kottenforst forest still belonged to the Ahrgau), especially after the dissolution of the Odangau.

The Ahrgau is mentioned in the records under various names including Arisco (880), pagus Aroensis (882), Argowe (1064) and Archgouwe (1065).