Founded in the 13th century on the southwest coast, Turku is Finland's oldest city and was also the country's first capital. The city, which has a population of around 195,000, is located at the mouth of the Aurajoki river. Turku Cathedral is the city's most recognizable landmark and is also Finland's national treasure. The cathedral, whose construction began in the late 13th century, is Finland's oldest surviving church and the most important example of medieval church architecture. Many old buildings were destroyed in the city fire in 1827, which is why the cityscape is predominantly modern. The old part of Turku was not destroyed, it consists mainly of wooden houses. In front of the city is the archipelago with an extensive archipelago of an estimated 20,000 to 50,000 islands. As part of the Baltic Sea off the southwest coast of Finland, the archipelago sea lies between the Finnish mainland and the Åland archipelago, bordered by the Gulf of Finland to the south and the Gulf of Bothnia to the north. The archipelago in the Archipelago Sea is commonly referred to as the "Turku Archipelago" after the city of Turku.