In this paper, the author examines two contemporary Byzantine-Greek sources on one episode of the last Byzantine-Sasanian war (602-628), the siege of Tbilisi in 627 (?) CE by the combined forces of Heraclius, the Byzantine Emperor, and those of a West-Turkic (called “Khazar”) leader. Two of the sources are Byzantine-Greek, one by Theophanes the Confessor who wrote between 811-3 and based himself, for the siege of Tbilisi, on a source not later than ca. 720 CE, and one by Theophanes’ contemporary Nicephoros the Patriarch, whose source was different; another source is an Armenian chronicle from Caucasian Albania attributed to Movsēs Dasxuranc‘i/Kałankatuac‘i, who wrote between the first years of the eighth century (very close to the time of Theophanes’ source) and 958 CE and whose version of the events is the fullest, but badly arranged by a later editor; then come two Georgian versions, that of the “Life of Kartli” and that of the older “Conversion of Kartli”. The conclusion of the author is that the Albano-Armenian author worked, while describing the siege of Tbilisi and the role of the Western Turks, from more than one source.