According to the simplified Byzantine idea, which was never discarded, the Byzantine basileus is the God's elected ruler. He is the only legitimate emperor in the world because he is the legitimate heir of Roman emperors. Apart from Byzantium, a series of other sovereign states existed throughout the Middle Ages on the territory of the former Roman Empire. That condition lead to the formulation of a sustainable interpretation of the conjured hierarchy of rulers and states. At the top of the fictitious ladder stood only the Byzantine emperor, and, at its bottom, rulers of the lowest rank to whom the emperor issued "orders". All other rulers were distributed between these two instances along the fictitious ladder of hierarchy, depending on their power and the esteem they enjoyed. At the same time, the Byzantine basileus was also perceived as the "spiritual parent" of the Christian nations and rulers who, on the otherhand, depending on their esteemed, boasted varying degrees of "spiritual kinship" with the emperor. These Byzantine concepts were adopted by Stefan Nemanja and his heirs, so that, at times, in medieval Serbia they were real and not fictitious. In the last decades of the XIV century, the power and esteem of Byzantium waned rapidly. The Empire had to take on difficult obligations towards the Ottoman Turks of which she was freed only after the Battle of Ankara (1402). The liberation from demeaning commitments brought on a revival of the ever present concept of ideal supremacy of the Byzantine emperor, especially among rulers in the Balkans. Such ideas were adopted by Constantine of Kostenec, the author of the Vita of Stefan Lazarevic, who, however, added certain corrections, conforming them to the views of the Serbian spiritual elite. According to the treaty of Gallipoli, sultan Suleiman accepted (1403) emperor Manuel II Palaiologos as his "father", a fact known also to Constantine the Philosopher, as was later also repeated by sultan Mehmed I. At the time when, in 1410, Stefan Lazarevic received for the second time the crown of despots from Manuel II, relations between the Byzantine basileus and the Serbian despots were defined as those of "father and son". By those means, Constantine the Philosopher elevates the position of the Serbian ruler to the level once held by king Milutin following his marriage to Simonis. The author of the Vita of Stefan Lazarevic took strict care to state the noble rank of the Serbian despots and thus matched it with those of sultan Mehmed I and the contender to the throne, Musa, who addressed the despots as "brother". Constantine the Philosopher makes no mistake either when referring to the king of Hungary and emperor of the Holy Roman Empire, Sigismund, whose vassal Stefan was. Regardless, of such ties between the two rulers, Sigismund is never mentioned as the despots' "parent" but solely as his "comrade"(ally), probably because the Hungarian king belonged to the oicumene of Western and not Eastern Christianity and could thus by no means have been a "spiritual parent" to the Orthodox Serbian despots.
The terminology of kinship and hierarchy of rulers in the writings of Constantine the Philosopher and his contemporaries
