Nyborg (nüˈbôr) [key], city (1992 pop. 15,352), Fyn co., S central Denmark, a seaport at the head of Nybord Fjord (an arm of the Store Bælt). It is an industrial center, with shipyards and plants manufacturing textiles and tobacco products. In Nyborg castle, built to control the Store Bælt (c.1170; now in ruins) Eric V granted (1282) the first Danish constitution. It was a royal capital (1200–1430).