In 1996 silver treasure was found in a pasture at the hamlet of Westerklief. It has been dated to the 9th century and is attributed to Vikings, who likely had an operating base there. The treasure is approx. 1.7 kilograms of silver coins and jewels, and small silver ingots. It now can be seen in the Rijksmuseum voor Oudheden in Leiden. Some years later smaller silver treasures from the same period were found in this area, confirming the theories of origin. Wieringen became an island around 1200 as a result of successive storm floods that surrounded it with water. This status lasted for more than 700 years.