Altenburg (listen) is a city in Thuringia, Germany, located 40 kilometres (25 miles) south of Leipzig, 90 kilometres (56 miles) west of Dresden and 100 kilometres (62 miles) east of Erfurt. It is the capital of the Altenburger Land district and part of a polycentric old-industrial textile and metal production region between Gera, Zwickau and Chemnitz with more than 1 million inhabitants, while the city itself has a population of 33,000. Altenburg was first mentioned in 976 and later became one of the first German cities within former Slavic area, east of the Saale river (as part of the medieval Ostsiedlung movement). The emperor Frederick Barbarossa visited Altenburg several times between 1165 and 1188, hence the town is named a Barbarossa town today. Since the 17th century, Altenburg was the residence of different Ernestine duchies, of whom the Saxe-Altenburg persisted until the end of monarchy in Germany in 1918. Industrialization reached Altenburg and the region quite early in the first half of the 19th century and flourished until the Great Depression around 1930. Economic malaise set in while Altenburg was in East Germany and continued after German reunification in 1990, evidenced by a decline in population, high unemployment and house vacancy rates. The main sights of Altenburg are the castle, the Lindenau-Museum, the historic city center (most buildings are from early-modern origin) and the Gründerzeit architecture around the center. The popular German card game Skat was developed in Altenburg during the 1810s and the founder of the famous Brockhaus Enzyklopädie, Friedrich Arnold Brockhaus, lived and worked in Altenburg between 1810 and 1817. Altenburg lies in the flat and fertile landscape of Osterland on the Pleiße river in the very east of Thuringia, next to the neighboring federal state of Saxony.