Built as a fortress after Viking attacks in the early Middle Ages, Het Steen is Antwerp's oldest building and used to be urban centre. It was used as a prison between 1303 and 1827. Much of it, including dozens of historic houses and the oldest church of the city, was demolished in the 19th century when the quays were straightened to stop the silting up of the River Scheldt. The remaining building contains a shipping museum. At the entrance bridge to the castle is a statue of two humans and a giant said to terrorise the citizens of the city in medieval times. .