A Prussian province lying between the Baltic and Brandenburg, with West Prussia on the E. and Mecklenburg on the W., is a flat and in some parts sandy country, with no hills, many lakes, and a large lagoon, the Stettiner Haff, into which the chief river, the Oder, falls; the islands of Wallin, Usedom, and Rügen belong to the province; the main industry is agriculture, principal products rye and potatoes; poultry-rearing and fishing are extensively carried on; there are shipbuilding, machine-works, sugar and chemical factories; Stettin, the capital, and Stralsund are important trading centres; a university is at Greifswald; the Slavic population embraced Christianity in the 12th century; shortly afterwards the duke joined the German Empire; after the Thirty Years' War much of the province fell to Sweden, and the whole was not finally ceded to Prussia till 1815.