Nidaros, Niðarós or Niðaróss (Old Norse pronunciation: [ˈniðɑˌroːsː]) was the medieval name of Trondheim when it was the capital of Norway's first Christian kings. It was named for its position at the mouth (Old Norse: óss) of the River Nid (the present-day Nidelva). Although the capital was later moved to Oslo (around the year 1300), Nidaros remained the centre of Norway's spiritual life until the Protestant Reformation.
https://en.wikipedia.org/wiki/Nidaros