Kalisz (käˈlēsh) [key], Ger. Kalisch, city (1993 est. pop. 106,600), Wielkopolskie prov., central Poland. An industrial center, it has factories producing textiles, clothing, chemicals, aircraft components, and paper. One of the oldest Polish towns, it has been identified as the Slavic settlement of Calissia mentioned in the 2d cent. A.D. by Ptolemy. It flourished as a trade center from the 13th cent. At Kalisz, Casimir III signed (1343) the treaty with the Teutonic Knights by which he conceded his rule over East Pomerania. The city passed to Prussia in 1793, was transferred to Russia in 1815, and was restored to Poland in 1919. In a treaty signed (1813) at Kalisz, Prussia and Russia formed an alliance against Napoleon I.