Theodore Syncellus was a prominent member of the clergy in Constantinople in the 620s, being a close advisor to Patriarch Sergius. As such he was chosen to participate in a delicate mission to the Avar khagan during the siege of the city in 626 and to deliver celebratory sermons. The first, ‘On the Robe’, commemorated the restoration of the miraculous relic of the Virgin’s Robe to the shrine at Blachernae, just outside the city walls, after it had been removed to protect it from Avar looting in 623. The second, ‘On the Siege’, analysed and gave thanks for the city’s escape from a joint attack by Avars and Persians in 626. The two speeches provide important evidence for popular devotion in the capital, especially to the Virgin Mary who now acquires the status of the city's special protector, for the role of Patriarch Sergius and others in leading the city during the long absence on campaign of the emperor Heraclius, and for how contemporary events could be fitted into Biblical contexts to elevate Constantinople and its inhabitants to the status of the new Israel. This new English translation of these two sermons (the first complete translation of 'On the Robe' and the first of 'On the Siege') sheds light on both the religious history of the eastern Roman Empire at the end of antiquity and on events in seventh-century Constantinople.