Fredericia (frĭħərēˈtsyä) [key], city (1992 pop. 28,529), Vejle co., central Denmark, on the Lille Bælt. It is a port, an industrial center, and an important rail junction. Manufactures include refined petroleum, chemicals, textiles, frozen fish, machinery, and tobacco. Fredericia was built in 1650 by Frederick III as the principal fortress on Jylland and was not permitted to expand beyond its ramparts. In 1849 the Danes defeated the Prussians there. The fortress was closed in 1909, and the city's modern development began.