Dagfinn was sent to Trondheim to announce King Haakon's ascension as part of the traditional process of proclaiming a new king in Norway. Trondheim, historically known as Nidaros, was a significant city in Norway and often served as a central location for important announcements and ceremonies related to the monarchy. The city held religious and political importance, being the site of the Nidaros Cathedral, which was a key religious center. Announcing the ascension of a new king in Trondheim would ensure that the news reached a wide audience and was recognized by influential figures in the region, thereby solidifying the new king's legitimacy and authority.