The first Serbian record of the assassination of the Ottoman Sultan Murad I was the "Life of Despot Stefan Lazarević" by Constantine of Kostenets, although the name of the executor was not mentioned. The heroic image of the Battle of Kosovo and the cult of Lazar's martyrdom has lost its force over time. The epic expression of the Battle was cultivated in the emigration of Serbs to the mountainous regions of Old Serbia, Montenegro and Herzegovina. Following the Fall of Constantinople (1453), three thousand Serbs began a nomadic life. In these regions, the image of the Kosovo hero was cultivated and preserved. The figure of Murad's assassin probably originated in the culture of exile, where his heroic deed could inspire constant resistance to the Turks. The Byzantine historians from the 15th century, Doukas and Laonikos Chalkokondyles also wrote about the Battle and about "sacrifice of a Christian nobleman who killed the Sultan in his tent". Serbian soldier and author of a memoir Konstantin Mihailović was the first to mention the name of Miloš Obilić in his work the "Memoirs of a Janissary" (ca. 1497), while he also described the betrayal of Vuk Branković. An anonymous resident of Dubrovnik or Dalmatia translated Doukas' parts about the Battle of Kosovo, citing the moment of the betrayal, but attributed it to Dragoslav Pribišić. Italian literature and popular poetry in Republic of Ragusa influenced educated Serbian exiles to produce the first "bugarštice" based on the accumulation of oral history in the late 15th century. Some of the "bugarštice" cultivated the Kosovo Legend.