There is one intriguing line of argument to suggest that the Slav presence in Kosovo and southernmost part of the Morava valley may have been quite weak in the first one or two centuries of Slav settlement. Only in the ninth century do we see the expansion of a strong Slav (or quasi-Slav) power into this region. Under a series of ambitious rulers, the Bulgarians – a Slav population which absorbed, linguistically and culturally, its ruling elite of Turkic Bulgars – pushed westwards across modern Macedonia and eastern Serbia, until by the 850's they had taken over Kosovo and were pressing on the border of Rasci.