Siege of Onoguris
555 CE.
Shown on the map at 42.297°, 44.460°.
The siege of Onoguris occurred in 554 or 555 AD during the Lazic War between the Byzantine Empire and the Sasanian Empire. The Byzantine generals led by Martin needed to score a quick victory on the battlefield to redress their assassination of the Byzantine ally King Gubazes II of Lazica. They launched a full-scale assault on the new Sasanian fort at Onoguris, which was located near the main Byzantine stronghold of Archaeopolis. The arrival of a small relief force under the new Sasanian commander Nachoragan turned the tide of the battle and resulted in an easy victory for the Sasanians instead. The Byzantines subsequently abandoned their base at Archaeopolis also, which was then destroyed by the Sasanians who now gained momentum.
Text from the Wikipedia article Siege of Onoguris, licensed CC BY-SA 4.0.