Oslo is the capital and most populous city of Norway. It constitutes both a county and a municipality. During the Viking Age the area was part of Viken, the northernmost Danish province. 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 the king's honour. It was established as a municipality (formannskapsdistrikt) on 1 January 1838. The city functioned as the capital of Norway during the 1814–1905 union between Sweden and Norway. From 1877, the city's name was spelled Kristiania in government usage, a spelling that was adopted by the municipal authorities only in 1897. In 1925 the city, after incorporating the village retaining its former name, was renamed Oslo. In 1948 Oslo merged with Aker, a municipality which surrounded the capital and which was 27 times larger, thus creating the modern, vastly enlarged Oslo municipality.