The siege of Phasis took place in 555–556 during the Lazic War between the Byzantine and Sasanian Empires. Expecting an easy victory, the Persians besieged the town of Phasis in Lazica, held by the Byzantines, but were defeated in the ensuing irregular battle. The main source for the siege is the 6th-century historian Agathias.
Background
The Lazic War had started in 541 with the defection of the Lazi under their king Gubazes II from Byzantium to Persia. The Persians quickly overran the country, but after Gubazes learned that the Persians planned to kill him, deport his people, and bring in Persian colonists, he asked the Byzantines for help.
In 554, the Persians won a major victory against the Laz-Byzantine forces at Telephis, forcing the latter to withdraw to the western parts of the country, and in the next year they were able to thwart a Byzantine attack on the fortress of Onoguris. In the spring of 555, the Persian general Nachoragan took the initiative in besieging the major Laz-Byzantine stronghold, the town of Phasis, which lay at the mouth of the namesake river.
Opposing forces and preparations for the siege
Nachoragan led an army of ca. 60,000 men. The Byzantine forces of the area were led by the magister militum per Armeniam Martin and his second-in-command Justin, son of Germanus. Their combined forces were less than 20,000 men. Nachoragan could expect an easy victory as the town and its fortifications were built of wood and were vulnerable to fire.
The town's location between the Black Sea and the River Phasis secured it from the east, north, and west. At its south side, a moat was its first line of defense. Nachoragan's forces however emptied the moat after days of hard work, and managed to surround the town from its river side too by building a bridge of boats across the Phasis. Meanwhile, the Byzantines had organized the defense of the city, with their forces taking their places at the various sides of the fortifications.
The extreme western side, the one closest to the river, was guarded by Justin, while Martin positioned himself in the south-western side. The south side was defended by Angilas, Theodore, and Philomathius. Angilas is recorded leading a regiment of Moorish peltasts and spearmen, probably meaning they were only armed with shield and lances. Theodore led heavy infantry consisting of Tzani, a recently Christianized tribe living in the mountains above Trapezus, while Philomathius led Isaurian slingers and dart-throwers. The south-eastern side was guarded by Gibrus, who led a combined force of Heruli and Lombards. The extreme eastern side was guarded by Valerian, leading forces from the praetorian prefecture of the East. Their composition is not recorded. Finally, the Byzantine ships were placed under the protection of Dabragezas the Wend and Elmingir (Elminegeir) the Hun.
Siege
Operations started with a volley of arrows from the Persians. Martin, the overall commander of the Byzantine troops, had given instructions to the whole army to stay at their respective posts. They were to disregard attempts by the Persians to induce them to sally forth from the fortifications and fight in the open. However, Angilas and Philomathius with about two hundred of their men opened a town gate, exited the town and attacked the nearest force of Sassanids whose archers were harassing the defenders. Theodore at first attempted to restrain them, but then bowed down to "majority opinion" and followed them in attacking. He was reportedly reluctant to violate orders, but unwilling to be branded a coward by the soldiers.
The Byzantine force was heavily outnumbered, and Agathias reports that they "would almost certainly have been annihilated", but they were saved by an error of the Dailamites. The Dailamites were a force of auxiliaries, originating in the mountains of Persia. "They fought on foot, armed each with a sword, a shield, and three javelins". They decided against attacking the Byzantines from a distance, and instead they "calmly awaited their approach" and then easily performed an encirclement. The encircled Byzantines however began a desperate attack on the enemies positioned closer to the town walls, and the Dailamites "opened up their ranks and made way from them" instead of standing their ground. Thus Angilas and the others escaped back to the safety of the city.