King Olav Haraldsson was buried by Nidelven, the river Nid, after he was killed in the battle of Stiklestad in1030.
Tradition has it that the high Altar of the Cathedral now stands on the exact spot of this burial site. One year and five days after he died the King was declared a saint, and pilgrims began to flock to Nidaros and the King’s grave.
The national sanctuary of Norway, built over the grave of St. Olav. Work began in 1070, but the oldest parts still in existence date from the middle of the twelfth century. These are in the Romanesque style, while most of the cathedral is Gothic in style. The building was completed in about 1300, but after being damaged several times by fire, it lay largely in ruins at the time of the Reformation in 1537. In 1869 extensive restorations were begun, and a century later it was again restored to its original grandeur. READ more about Trondheim: Nidaros Cathedral
Source: trondheim.com / Norway Today