Nidaros in the context of Diocese of Nidaros

Trondheim (UK: /ˈtrɒn(d)haɪm/ TRON(D)-hyme, US: /ˈtrɒnheɪm/ TRON-haym; Urban East Norwegian: [ˈtrɔ̂nː(h)æɪm]; Southern Sami: Tråante), historically Kaupangen, Nidaros, and Trondhjem (locally [ˈtrɔ̂nːjæm] ), is a city and municipality in Trøndelag county, Norway. As of 2025, it had a population of 216,518. Trondheim is the third most populous municipality in Norway, and is the fourth largest urban area. Trondheim lies on the south shore of Trondheim Fjord at the mouth of the River Nidelva. Among the significant technology-oriented institutions headquartered in Trondheim are the Norwegian University of Science and Technology (NTNU), the Foundation for Scientific and Industrial Research (SINTEF), the Geological Survey of Norway (NGU), and St. Olavs University Hospital.

The settlement was founded in 997 as a trading post and served as the capital of Norway through the Viking Age until 1217. From 1152 to 1537, the city was the seat of the Catholic Archdiocese of Nidaros; it then became, and has remained, the seat of the Lutheran Diocese of Nidaros and the site of the Nidaros Cathedral. The city was incorporated in 1838. The current municipality was formed in 1964, when Trondheim merged with Byneset Municipality, Leinstrand Municipality, Strinda Municipality, and Tiller Municipality, and further expanded on 1 January 2020, when Trondheim merged with Klæbu Municipality.

Saint Olaf (c. 995 – 29 July 1030), also called Olaf the Holy, Olaf II, Olaf Haraldsson, and Olaf the Stout or "Large", was King of Norway from 1015 to 1028. Son of Harald Grenske, a petty king in Vestfold, Norway, he was posthumously given the title Rex Perpetuus Norvegiae (English: Eternal/Perpetual King of Norway) and canonised at Nidaros (Trondheim) by Bishop Grimketel, one year after his death in the Battle of Stiklestad on 29 July 1030. His remains were enshrined in Nidaros Cathedral, built over his burial site. His sainthood encouraged the widespread adoption of Christianity by Scandinavia's Vikings/Norsemen.

Pope Alexander III confirmed Olaf's local canonisation in 1164, making him a recognised saint of the Catholic Church, and Olaf started to be known as Rex Perpetuus Norvegiae – eternal king of Norway. Following the Reformation, he was a commemorated historical figure among some members of the Lutheran and Anglican Communions.

The Archdiocese of Nidaros (or Niðaróss) was the metropolitan see covering Norway in the later Middle Ages. The see was the Nidaros Cathedral, in the city of Nidaros (now Trondheim). The archdiocese existed from the middle of the twelfth century until the Protestant Reformation.

The history of Norway has been influenced to an extraordinary degree by the terrain and the climate of the region. About 10,000 BC, following the retreat inland of the great ice sheets, the earliest inhabitants migrated north into the territory which is now Norway. They traveled steadily northwards along the coastal areas, warmed by the Gulf Stream. They were hunter-gatherers whose diet included seafood and game, particularly reindeer as staple foods. Between 5,000 BC and 4,000 BC the earliest agricultural settlements appeared around the Oslofjord. Gradually, between 1,500 BC and 500 BC, agricultural settlements spread to the entire south Norway, while the inhabitants of the regions north of Trøndelag continued to hunt and fish.

The Neolithic period started in 4,000 BC. The Migration Period caused the first chieftains to take control and hilltop forts to be constructed. From the 8th century Norwegians started expanding across the seas to the British Isles and later Iceland and Greenland. The Viking Age also saw the unification of the country. Christianization was completed during the 11th century and Nidaros became an archdiocese. The population expanded quickly until 1349 when it was halved by the Black Death and successive plagues. Bergen became the main trading port, controlled by the Hanseatic League. Norway entered the Kalmar Union with Denmark and Sweden in 1397.

The Bjarkey laws (Old Swedish: biærköa rætter, Old Icelandic: bjarkeyjar-rettr, Norwegian: bjarkøretten, Danish: bjærkeret, birkeret) were the laws and privileges of medieval Scandinavian merchant towns (birks).

In Norway, the Bjarkey laws concerned all the merchant towns and also every location with trade, such as fishing villages and market locations. There are two versions, an early and a late Bjarkey law, of which the early one only remains as fragments and concerned the merchant town of Nidaros. The later Bjarkey law was created primarily for the merchant town of Bergen and only the most necessary amendments were made for other merchant towns. The extant manuscripts are very much in agreement, even when they explicitly concern different merchant towns. The late law was accepted at a ting in Bergen in 1276, and is divided into nine sections of which the last one, the Farmannalög is a kind of sea law. This was the first of the revised City Laws of Magnus VI of Norway (1238-1280), known as Magnus Lagabøtes bylov, and integrated into the national Magnus Lagabøtes landslov.