In the present article we discuss one of the key and final episodes of the military confrontation between the Byzantine Empire and Sassanid Iran which took place in the Lazica Kingdom, in particular, liberation in 551 by the Byzantines of the last foothold -the Petra fortress. This is examined on the basis of analysis of material obtained as a result of archaeological excavations in Petra-Tsikhisdziri (south western Georgia) carried out at different times and mostly in 2016-2020. Recent archaeological discoveries have produced more knowledge about the besiegement of Petra. This includes information on who was defending the fortress, what the garrison looked like, how it was equipped and supplied, how the siege was developed and finalized, etc. The significance of the findings and their consideration together with the written sources are very important to finally identify the city-fortress Petra, reinforced by the Byzantines, with modern Tsikhisdziri -an issue which is still debatable among the scholars.