This 9th-century waterfront fortress, built to protect the western frontier of the Holy Roman Empire, was partially rebuilt 700 years later by Emperor Charles V. You can distinguish the darker, medieval masonry extending midway up the walls from the lighter upper level of 16th-century work. The only survivor of the original waterfront was used as a prison for centuries. Opposite the entrance is a cross where those sentenced to death said their final prayers. Many houses were torn down in the 19th century to make room for the wide, straight quays that today are practically deserted, the port having moved north of the city. The Noorderterras, a promenade starting at the Steen, is a popular place for a Sunday stroll along the Scheldt, which here is 550 yards wide. "God gave us the river," say Antwerpers, "and the river gave us all the rest." The Steen now houses a pleasant café and a small children's museum (open Tues.–Sun. from 10–6).