The size of this inland sea remained largely stable from the 15th century onwards due to improvements in dikes, but when storms pushed North Sea water into the inlet, the Zuiderzee became a volatile cauldron of water, frequently resulting in flooding and the loss of ships. For example, on 18 November 1421, a seawall at the Zuiderzee dike broke, which flooded 72 villages and killed about 10,000 people. This was the Second St. Elizabeth's flood.