Slagelse, city, Sjælland (Zealand), Denmark. One of the oldest towns in Denmark (chartered 1288) and a prosperous trade centre in the Middle Ages, it retains few signs of antiquity, due to repeated fires. The commercial centre of western Sjælland, its industry includes vegetable and meat canning. The famous fortress of Trelleborg (about 5 miles [8 km] west-southwest) is one of the most important Viking remains in Denmark. Pop. (2008 est.) city, 31,879; (2005 est.) mun., 76,185.