Silesia (4,224), a province of South-East Prussia, stretching S. between Russian Poland (E.) and Austria (W. and S.); the Oder flows NW. through the heart of the country, dividing the thickly forested and in parts marshy lands of the N. and E. from the mountainous and extremely fertile W.; rich coal-fields lie to the S., and zinc is also a valuable product; agriculture and the breeding of cattle, horses, and sheep flourish, as also the manufacture of cottons, linens, &c.; Breslau is the capital; for long under the successive dominions of Poland and Bohemia, the Silesian duchies became, in the 18th century, a casus belli between Austria and Prussia, resulting in the Seven Years' War (q. v.) and the ultimate triumph of Frederick the Great of Prussia.