Oslo is the capital and most populous city of Norway. It constitutes both a county and a municipality. As of 23 November 2020, the municipality of Oslo had a population of 697,549, while the population of the city's greater urban area was 1,019,513, as of 4 November 2019. The metropolitan area had an estimated population of 1.71 million.
During the Viking Age the area was part of Viken. Oslo was founded as a city at the end of the Viking Age in the year 1040 under the name Ánslo, and established as a kaupstad or trading place in 1048 by Harald Hardrada. The city was elevated to a bishopric in 1070 and a capital under Haakon V of Norway around 1300. Personal unions with Denmark from 1397 to 1523 and again from 1536 to 1814 reduced its influence. After being destroyed by a fire in 1624, during the reign of King Christian IV, a new city was built closer to Akershus Fortress and named Christiania in honour of the king. It became a municipality on 1 January 1838. The city functioned as the capital of Norway during the 1814–1905 union between Sweden and Norway.