Siege of Constantinople: A horde of Avars, consisting of about 80,000 men, attack the walls of Constantinople. A small Persian army arrives on the Bosphorus, on the Asiatic side. The Theodosian Walls are stormed with the most up-to-date siege equipment, in the form of traction trebuchets. The Avars have also mobile armoured shelters and siege towers; the latter are covered in hides for fire protection. The defense of the capital is in the hands of Patriarch Sergius I and Bonus.
July 31 - The Avars and Persian allies under Shahrbaraz launch an attack along the entire length of the Theodosian Walls ; the main effort is concentrated against the central section, particularly the low-lying mesoteichion. After a fierce infantry battle on the walls, the Byzantine army holds off many assaults on the city. Emperor Heraclius makes arrangements for a new army under his brother Theodore to operate against the Persians in western Anatolia, while he returns to his own army in Pontus.
Byzantine–Persian War: Heraclius, his army reduced by campaigning to less than 30,000 men, is on the defensive in Pontus. Apparently he leaves a strong Byzantine garrison in Trapezus, and withdraws north-eastward along the Black Sea into Colchis, where he halts the Persians by aggressive defensive-offensive operations along the Phasis River. By attracting the Persian army under Shahin Vahmanzadegan in Anatolia, he provides Theodore with the opportunity to defeat them. By the end of the summer he threatens the communication of the Persians at Chalcedon.
Winter - Heraclius makes an alliance with Tong Yabghu Qaghan, ruler of the Western Turkic Khaganate, for a joint invasion of the Persian Empire the following spring. He promises his daughter Eudoxia Epiphania, age 15, in marriage to Tong Yabghu and sends her under escort with wondrous gifts.
King Edwin of Northumbria defeats the West Saxons under Cynegils, who has tried to thwart the growing strength of Edwin by having him assassinated. Edwin obliges Cynegils to acknowledge Northumbria's supremacy.
Summer - King Khosrau II plans an all-out effort against Constantinople. He returns to Anatolia with two armies of unknown size, presumably more than 50,000 men each. One of these is to contain Heraclius in Pontus; another under Shahin Vahmanzadegan is defeated by Theodore.
Asia
July 2 - Li Shimin travels to the Tang capital Chang'an to bid farewell his younger brother Li Yuanji, who has been given command of a Chinese expedition against the Eastern Turkic Khaganate. Hearing of a plot to murder him, he and a few supporters seize the northern entrance to the emperor's palace. Li Shimin ambushes and eliminates his rival brothers Li Yuanji and Li Jiancheng, in the Xuanwu Gate Incident.
September 4 - Emperor Gao Zu abdicates in favor of his son Li Shimin after an 8-year reign. He passes the throne to him.
