The epic tale of Cid emerged and had been developing in the period from XII to XIV century A. D. We know it in various forms, including epic, chronicles, and romances. One of the main questions in its analysis is the problem of oral and/or written genesis of a given fragment in the hero’s biography. Throughout the long history of the tale existence, the image of Cid has been considerably transformed; the most definitive change occured in the process of adding the story of the young Rodrigo’s exploits to the contents of the Song of My Cid. It became the main topic in the later poems, historicized biographies of the hero, and romances. The beginnings of Cid’s heroic biography have engaged him into service to the king Fernando I; the hero himself starts to show some rebelliousness towards king’s sons (his actions as well as advices incur their constant displeasure). This fragment of the tale has been retold in the History of Spain (more specifically, its so called versión crítica existed under the title Crónica de veinte reyes) and were not preserved in poetical form. Hence, its (presumably, epic) source camn be established only by the method of reconstruction. In the paper, an attempt of such reconstruction is undertaken, based on the principles of epic plot making.