Essen is the second largest city of the Ruhr Area and one of the largest cities in Germany. The city was founded in the 9th century and thanks to the Krupp family has become one of the most important coal mining and steel production centers of the country. After the region-wide decline of heavy industry in the 80's the city has gradually developed the tertiary sector and converted the coal mines into museums. The most notable example is the Zollverein Coal Mine Industrial Complex, which used to be Europe's largest of its kind. Essen also has several museums and parks, as well as churches and the Old Synagogue, which attract numerous tourists every year.