Vineta is a mythical sunken city off the German or Polish North Sea Coast. I was suprised to find out that the first mention of Vineta can be found in the travel writings of Ibrahim ibn Yaqub from around 960 CE. According to historians, Ibn Yaqub was a traveler and merchant from a jewish-seraphim family from Spain, who converted to Islam and who traveled extensively through Northern Europe. He wrote in arab and gave the first reliabel accounts of the Polish and Viking societies. He mentions a city called “Weltaba” – in modern Polish “WeÅ‚tawa” translates roughly as “place among waves” – and which he describes as the largest city in Europe, close to the sea and with twelve gates, located in the farthest north-west corner of what is today Poland.
There are other accounts about such a northern metropolis from the 10. and 11. Century AD. But mentions cease after around 1.170 AD. Today it is assumed that Vineta, or Weltaba, is not one city but rather that the myth actually combines the historic events around two cities and political centers of that era: Jaromarsburg (Arkona) and Wolin or Vimne. Both cities were either destroyed or deserted at the beginning of the 11 Century AD and both were powerful and wealthy cities. It took another 600 years for Vineta to reappear on several maps, but this time as a myth or a historical speculation.

For more information see also:
http://vineta.eiszeitland.de/wineta.htm
and the other posts here!