2 – Sassanid Persians & Avars (626)
The siege of 626 is better documented than the events of 559 and it involved a huge force of 80,000 men, comprised of Avars, Slavs, and Persians. The war between the Byzantines and Sassanids had dragged on since 602 with no clear advantage to either side although both empires were massively weakened by the fighting. By the seventh century, the Avars, a group of Eurasian nomads, were another threat to the Empire. They were defeated by the Byzantines in 619 but returned seven years later on a mission to destroy their enemies.
The city of Constantinople was ripe for conquest in 626 as Emperor Heraclius was away in eastern Anatolia in a campaign against the Persians. There was a riot in the city in May because one of Constantinople’s leaders wanted to cut bread rations and also increase the price of bread. The Persian leader, Khosrau, sensed an opportunity and recruited two armies in a bid to end the war once and for all.
Khosrau coordinated the attack with the leader of the Avars; the Persians would attack from the east, and the Avars would hit the city from the west. Since the Byzantine navy controlled the Bosporus Strait, the Persians could not send reinforcements to the Avars. This proved crucial because while the Persians were siege warfare experts, the Avars were not.
The assault began on June 29 as 12,000 expertly trained Byzantine troops guarded the city. Led by Bonus and Sergius, the defenders held off the enemy for over a month. Morale remained high as the inhabitants believed that they were under divine protection. After multiple failed assaults, the raiders were forced to flee when the Persian and Avaric fleets were sunk in different fights. The siege was effectively over on August 7, and three days later, the Avars burned their siege engines and withdrew.