While Arno was in Rome attending to some of Charlemagne's business in 798, Pope Leo III appointed him Archbishop over the other bishops in Bavaria (Freising, Passau, Regensburg, and Säben). When the dispute over the church's border between Salzburg and Aquileia broke out, Charlemagne declared the River Drave to be the border. Arno also began the copying of 150 volumes from the court of Charlemagne. This was the start of the first library in Austria.