Agathias, born around 532 and died after 579, is one of the most important writers of the Byzantine history because the information given in his work is not found in other sources. The author, who was a lawyer interested in the art of poetry, later on decided to write history with the encouragement of the people around him. His ―History‖, reached us in five books, covers only seven years between A.D. 552-559. Of the events of these years, it deals almost exclusively with the military campaigns in Italy and Lazica, which took place during the final stages of Justinian‘s reign. Agathias‘ scale is large, and he does not make do with simple narrative: at least a third of the work is occupied with scholarly or personal digressions extraneous to the main theme. Of them, in particular, the stories about the old histories of Frankish and Persian are regarded as an original source. Although being a Christian, Agathias gives little space for religious elements in his writing style, and presents very important information about the Turks in his work. Among the Turkish tribes that Agathas gives information about are Huns, Avars, Onogurs, Sabirs, Ephthalites, Kutrigurs and Utigurs. In these tribes, especially the information related Sabirs and Kutrigurs-Utigurs have unprecedented value in terms of Turkish history. In addition, the author, who also informes us about Turkish commanders in the Byzantine army, sometimes talks about the military tactics and cultural structures of the Turks and gives information that does not exist in other sources. Therefore, the work of Agathias is a very important resource not only for Turkish but also for European and Iranian history.

Keywords: Agathias, Turks, Huns, Avars, Onogurs, Sabirs, Ephthalites, Kutrigurs, Utigurs