De Zijpe en de Zuiderzee

The Zijpe and the Zuiderzee Dutch geologists and archaeologists disagree about the time the Flevo-lakes in the Wet Heart of the Netherlands were connected with the western part of the Waddenzee. Geologists hold the strong view that this connection originated in the centuries bc. Archaeological research revealed, however, that the pre-urban development of the city of Amsterdam did not start until the last quarter of the 12th century ad. This urban development has been considered as an indication that the shipping route between the mouth of the river Amstel and the Waddenzee had improved shortly before. Therefore, archaeologists are convinced that the improvement of this shipping route was forced by the All Saint’s flood of 1170. To the west of Schagen, the sea is considered to have broken up the coastal barrier which led to the development of the Zuiderzee. Because of the etymological relation between the names Flevo and Vlie, the Flevo-lakes must have been already connected with the Waddenzee in the Roman period. Near Medemblik, however, the water did not become brackish before the 8th century ad and more to the south not earlier than the 9th century. Therefore, drainage must have been the main function of the connection between the Flevo-lakes and the Waddenzee for centuries. From historical documents it is known that somewhere around Stavoren a large amount of land was lost to the sea in 1170. Together with the swift development of Amsterdam it is likely that the Zuiderzee came into being after 1170. A breakthrough of the coastal barrier to the west of Schagen at that time, however, is unlikely. In 1170 there was some damage in the northern part of the province of Holland caused by a storm surge, but the loss of land was limited due to the building of several dikes.