In the 13th century, the later Netherlands were still split into many smaller states, of which Holland was the most important one. One ruler of them, Wilhelm of Holland, who died in 1256, made it Roman king. In the year 1287, a great flood swallowed lots of lands in the Netherlands, creating the Zuider Zee, which made it possible for Amsterdam to become an important harbor later. In 1331, Gerhard III of Holstein (the strong man in Denmark) married countess Margarethe of Holland, Zeeland and Hennegau (part of Wallonia).