Nyborg, city and port, eastern Funen island, Denmark, on the Great Belt and Nyborg Fjord. Named for the castle (borg) built in 1170 to protect the Great Belt and chartered in 1292, it was the favourite meeting place of the Danehof (assembly of nobles and clergy) from 1282 to 1413. The Great Charter, Denmarkâs first constitution, was issued there in the former year. A large Swedish army surrendered outside the city in 1659. The castle, birthplace (1481) of King Christian II, was restored in 1923 as a museum. Nyborg was the terminus for the ferry to Zealand, but, with the opening of a tunnel and bridge system across the Great Belt in the late 1990s, traffic now passes north of the city. The city has a large plant that handles chemical waste. Pop. (2008 est.) city, 16,467; (2005 est.) mun., 31,009.