A
Slavic fortification stood at the mouth of the
Rhin on the northern shore. In the 12th century, the German settlement of Ruppin (now called
Altruppin) was established next to it. A few decades later,
Neuruppin was established on the southwest shore. A mill was built in
Altfriesack, between the Ruppiner See and the Bützsee next to the Slavic settlement of
Wustrau. The latter is probably the oldest settlement on the lake. Around the lake are other villages, which mostly now belong to the municipality of Neuruppin. Wustrau and Altfriesack now form one division in the municipality of
Fehrbellin. ==Economic and strategic importance==