Silesia (saɪˈliːʒə,saɪˈliːʃiə, also UK-iːziə, US-iːʒiə,-iːʃə,_sɪˈ-; see below) is a historical region of Central Europe that lies mostly within Poland, with small parts in the Czech Republic and Germany. Its area is approximately , and the population is estimated at around 8,000,000. Silesia is split into two main subregions, Lower Silesia in the west and Upper Silesia in the east. Silesia has a diverse culture, including architecture, costumes, cuisine, traditions, and the Silesian language (minority in Upper Silesia). The largest city of the region is Wrocław.
Silesia is along the Oder River, with the Sudeten Mountains extending across the southern border. The region contains many historical landmarks and UNESCO World Heritage Sites. It is also rich in mineral and natural resources, and includes several important industrial areas. The largest city and Lower Silesia's capital is Wrocław; the historic capital of Upper Silesia is Opole. The biggest metropolitan area is the Upper Silesian metropolitan area, the centre of which is Katowice. Parts of the Czech city of Ostrava and the German city of Görlitz are within Silesia's borders.
Silesia's borders and national affiliation have changed over time, both when it was a hereditary possession of noble houses and after the rise of modern nation-states, resulting in an abundance of castles, especially in the Jelenia Góra valley. The first known states to hold power in Silesia were probably those of Greater Moravia at the end of the 9th century and Bohemia early in the 10th century. In the 10th century, Silesia was incorporated into the early Polish state, and after its fragmentation in the 12th century it formed the Duchy of Silesia, a provincial duchy of Poland. As a result of further fragmentation, Silesia was divided into many duchies, ruled by various lines of the Polish Piast dynasty. In the 14th century, it became a constituent part of the Bohemian Crown Lands under the Holy Roman Empire, which passed to the Austrian Habsburg monarchy in 1526; however, a number of duchies remained under the rule of Polish dukes from the houses of Piast, Jagiellon and Sobieski as formal Bohemian fiefdoms, some until the 17th–18th centuries.