The investigation is organized around the interpretation of the fragment from the «History of Rodrigo». It is Latin biography of the great Castilian noble man and knight Rodrigo Diaz de Vivar, also known as Cid or Campeador. The story about the cases of Cid’s expulsion by his lord king Alfonso VI gives an opportunity to reconstruct some important aspects of a phenomenon of the Castilian Feudalism of the 12th cen. Castilian society is interpreted as a complicated system, main elements of which were connected by the ties of Vassalage.