The family head of the Sasaki clan that had been appointed as Omi Shugo (Military Governor of Omi Province) during the Kamakura period over generations, Nobutsuna SASAKI divided Omi Province into four to order his four sons to inherit them, respectively.
鎌倉時代に近江守護に代々任じられていた佐々木氏の当主である佐々木信綱は、四人の息子に近江を分けて継がせた。