Stuttgart is the capital and largest city of the German state of. It is located on the Neckar river in a fertile valley locally known as the "Stuttgart Cauldron" an hour from the Swabian Jura and the Black Forest. Stuttgarts urban area has a population of 609,219, making it the sixth largest city in Germany. 2.7 million people live in the citys administrative region and another 5.3 million people in its metropolitan area, making it the fourth largest metropolitan area in Germany. The city and metropolitan area are consistently ranked among the top 20 European metropolitan areas by GDP; Mercer listed Stuttgart as 21st on its 2015 list of cities by quality of living, and the Globalization and World Cities Research Network ranked the city as a Beta-status world city in their 2014 survey. Since the 6th millennium BC, the Stuttgart area has been an important agricultural area and has been host to a number of cultures seeking to utilize the rich soil of the Neckar valley. The Roman Empire conquered the area in 83 AD and built a massive near Bad Cannstatt, making it the most important regional center for several centuries. Stuttgarts roots were truly laid in the 10th century with its founding by Liudolf, Duke of Swabia, as a stud farm for his warhorses. Overshadowed by nearby Cannstatt, the town grew steadily and was granted a charter in 1320. The fortunes of Stuttgart turned with those of the House of Württemberg, and they made it the capital of their county, duchy, and kingdom from the 15th century to 1918. Stuttgart prospered despite setbacks in the Thirty Years War and devastating air raids by the Allies on the city and its automobile production. However, by 1952, the city had bounced back and it became the major economic, industrial, tourism and publishing center it is today. Stuttgart is also a transport junction, and possesses the sixth-largest airport in Germany. Such companies as Porsche, Bosch, Mercedes-Benz, Daimler AG, Dinkelacker, and others are headquartered there. Stuttgart is unusual in the scheme of German cities. It is spread across a variety of hills, valleys and parks. This is often a source of surprise to visitors who associate the city with its reputation as the "cradle of the automobile". The citys tourism slogan is "Stuttgart offers more". Under current plans to improve transport links to the international infrastructure, the city unveiled a new logo and slogan in March 2008 describing itself as "". For business, it describes itself as "Where business meets the future". In July 2010, Stuttgart unveiled a new city logo, designed to entice more business people to stay in the city and enjoy breaks in the area. Stuttgart is a city with a high number of immigrants. According to Dorling Kindersleys Dorling, "In the city of Stuttgart, every third inhabitant is a foreigner." 40% of Stuttgarts residents, and 64% of the population below the age of five, are of immigrant background.