Around 850 rose Vijayalaya , made use of an opportunity arising out of a conflict between Pandyas and Pallavas , captured Thanjavur and eventually established the imperial line of the medieval Cholas . Around 850 , out of obscurity rose Vijayalaya , made use of an opportunity arising out of a conflict between Pandyas and Pallavas , captured Thanjavur and eventually established the imperial line of the medieval Cholas .