On 9 september 878 the Carolingian king Karlmann, father of the later king and emperor Arnulf, issued an instrument documenting the donation of some land in Carinthia to his favourite monastery Ötting in Bavaria. The object of the donation was the royal demesne of Treffen, north of Villach and west of the Ossiacher See. The instrument mentions Carinthia under its oldest name: Karantanien. Moreover it provides many important place names and information relevant to the history of transport. Finally the description of the boundaries of the royal demesne allows us to draw interesting conclusions on its size, nature and structure.