Stockholm is the capital of Sweden and the most populous city in the Nordic countries; The city is spread across a total of 17 islands on the coast in the southeast of Sweden at the mouth of Lake Mälaren, by the Stockholm archipelago and the Baltic Sea. The area has been settled since the Stone Age, in the 6th millennium BC, and was founded as a city in 1252 by a Swedish statesman Birger Jarl. It is also the capital of Stockholm County. Stockholm is the cultural, media, political, and economic centre of Sweden. The Stockholm region alone accounts for over a third of the countrys GDP, and is among the top 10 regions in Europe by GDP per capita. It is an important global city, and the main centre for corporate headquarters in the Nordic region. The city is home to some of Europes top ranking universities, such as the Stockholm School of Economics, Karolinska Institute and Royal Institute of Technology. It hosts the annual Nobel Prize ceremonies and banquet at the Stockholm Concert Hall and Stockholm City Hall. One of the citys most prized museums, the Vasa Museum, is the most visited non-art museum in Scandinavia. The Stockholm metro, opened in 1950, is well known for its decoration of the stations; it has been called the longest art gallery in the world. Swedens national football arena is located north of the city centre, in Solna. Ericsson Globe, the national indoor arena, is in the southern part of the city. The city was the host of the 1912 Summer Olympics, and hosted the equestrian portion of the 1956 Summer Olympics otherwise held in Melbourne, Victoria, Australia. Stockholm is the seat of the Swedish government and most of its agencies, including the highest courts in the judiciary, and the official residencies of the Swedish monarch and the Prime Minister. The government has its seat in the Rosenbad building, the Riksdag is seated in the Parliament House, and the Prime Ministers residence is adjacent at the Sager House. The Stockholm Palace is the official residence and principal workplace of the Swedish monarch, while the Drottningholm Palace, a World Heritage Site on the outskirts of Stockholm, serves as the Royal Familys private residence.