Marstrand is a seaside locality situated in Kungälv Municipality, Västra Götaland County, Sweden. It had 1,319 inhabitants in 2010. It has held city privileges since 1200. The most striking feature about Marstrand is the 17th-century fortress Carlsten, named after King Carl X Gustav of Sweden. The town got its name from its location on the island Marstrandsön.