Oslo (// OZ-loh; Norwegian: ( listen), rarely ) is the capital and most populous city of Norway. It constitutes both a county and a municipality. Founded in the year 1040, 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 and with Sweden from 1814 to 1905 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's name was spelled Kristiania from 1877 and 1897 by state and municipal authorities, respectively. In 1925 it was renamed Oslo.
Oslo is the economic and governmental centre of Norway. The city is also a hub of Norwegian trade, banking, industry and shipping. It is an important centre for maritime industries and maritime trade in Europe. The city is home to many companies within the maritime sector, some of which are among the world's largest shipping companies, shipbrokers and maritime insurance brokers. Oslo is a pilot city of the Council of Europe and the European Commission intercultural cities programme.
Oslo is considered a global city and was ranked "Beta World City" in studies carried out by the Globalization and World Cities Study Group and Network in 2008. It was ranked number one in terms of quality of life among European large cities in the European Cities of the Future 2012 report by fDi magazine. A survey conducted by ECA International in 2011 placed Oslo as the second most expensive city in the world for living expenses after Tokyo. In 2013 Oslo tied with the Australian city of Melbourne as the fourth most expensive city in the world, according to the Economist Intelligence Unit (EIU)'s Worldwide Cost of Living study.
As of 1 July 2017, the municipality of Oslo had a population of 672 061, while the population of the city's urban area was 942,084. The metropolitan area had an estimated population of 1.71 million. The population was increasing at record rates during the early 2000s, making it the fastest growing major city in Europe at the time. This growth stems for the most part from international immigration and related high birth rates, but also from intra-national migration. The immigrant population in the city is growing somewhat faster than the Norwegian population, and in the city proper this is now more than 25% of the total.
As of 1 January 2016, the municipality of Oslo had a population of 658,390. The urban area extends beyond the boundaries of the municipality into the surrounding county of Akershus (municipalities of Asker, Bærum, Røyken, Rælingen, Lørenskog, Nittedal, Skedsmo, Ski, Sørum, Gjerdrum, Oppegård); the total population of this agglomeration is 942,084. The city centre is situated at the end of the Oslofjord, from which point the city sprawls out in three distinct "corridors"—inland north-eastwards, and southwards along both sides of the fjord—which gives the urbanized area a shape reminiscent of an upside-down reclining "Y" (on maps, satellite pictures, or from high above the city).
To the north and east, wide forested hills (Marka) rise above the city giving the location the shape of a giant amphitheatre. The urban municipality (bykommune) of Oslo and county of Oslo are two parts of the same entity, making Oslo the only city in Norway where two administrative levels are integrated. Of Oslo's total area, 130 km2 (50 sq mi) is built-up and 7 km2 (2.7 sq mi) is agricultural. The open areas within the built-up zone amount to 22 km2 (8.5 sq mi).
The city of Oslo was established as a municipality on 3 January 1838 (see formannskapsdistrikt). It was separated from the county of Akershus to become a county of its own in 1842. The rural municipality of Aker was merged with Oslo on 1 January 1948 (and simultaneously transferred from Akershus county to Oslo county). Furthermore, Oslo shares several important functions with Akershus county.