The oldest town settlement in Europe is Lepenski Vir in Serbia (9500–7200BC) and the people there were thought to be descendants of the early European population of the Brno-Předmostí (Czech Republic) hunter gatherer culture from the end of the last ice age. As I understand these people had heavy skulls & were descended from Cro-Magnon man. Seems these were proto-Slavs anyway, so answer to your question is the Slavs have been there basically 'forever'.