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. The Archdiocese of Nidaros was separated from Lund (in Scania) by the papal legate Nicholas Breakspeare in 1152, and the shrine to Saint Olaf in Nidaros Cathedral was Northern Europe's most important pilgrimage site during the Middle Ages. Archbishop Olav Engelbrektsson led Norway in its attempted resistance against the Danish Reformation, and was forced into exile by King Christian III in 1537. The archdiocese was abolished and replaced with a Lutheran diocese.[1]