But in 627, Constantinople learned what a siege really meant. Persia and the Empire were then at war with each other; and while Heraclius was carrying the campaign into the enemy’s country, a Persian army had encamped at Chalcedon for the purpose of joining the Avars in laying siege to the capital.[[559]]
As the Byzantine fleet, however, commanded the Bosporus, the allies could not unite their forces, and the Avars were left to act alone. The undertaking proved too difficult for the barbarians, notwithstanding the vigour with which it was conducted, and the siege was raised. But before retiring, a troop of Avaric horse set itself to devastate the suburbs, and having fired the Church of SS. Cosmas and Damianus, and the Church of St. Nicholas, dashed into the open ground beside the Church of Blachernæ, intent upon devoting also that sacred edifice to the flames. For some reason, that purpose was not carried into effect, and the church escaped all injury. This marvellous deliverance enhanced, indeed, the reputation of the Theotokos, but it likewise aroused a sense of the danger to which her shrine was liable, and so the Government of the day ordered the immediate erection of a wall along the western side of the Blachernæ quarter, to place the church beyond the reach of hostile attack in future. The wall was known, until the erection of the Wall of Leo, as the Single Wall of Blachernæ (Μονοτείχος Βλαχερνῶν:[[560]] τεῖχος τῶν Βλαχερνῶν).[[561]]
The wall is flanked by three fine hexagonal towers, built towards their summit in brick, perhaps, as Dr. Paspates[[562]] suggests, in order to lighten the weight of constructions erected on marshy ground. They are among the finest towers in the circuit of the fortifications. The interior of the southernmost tower, the only one which can be safely examined, measures 32-½ by about 19 feet, and was in three stories. Upon the face of the tower is an inscription, in letters formed with pieces of marble, in honour of the Emperor Michael, probably Michael II.
Between the first and second towers is a gate, named the Gate of Blachernæ (πόρτα τοῦ Μονοτείχους τῶν Βλαχερνῶν),[[563]] after the quarter before which it stood.
General View of the Walls of the City From The Hill On Which The Crusaders Encamped in 1203.
It has been generally supposed that the Wall of Heraclius comprised not only the portion of the city walls just indicated, but the whole line of fortifications extending from the Kerko Porta to the Golden Horn.[[564]] The evidence on the subject is, however, in favour of the opinion that the Wall of Heraclius was only the portion of the fortifications before us. It is the extent implied in the description of the Heraclian Wall, as a wall erected to bring the Church of Blachernæ within the line of the city bulwarks.[[565]] That is an apt description of a wall extending from the foot of the Sixth Hill to the Golden Horn; it is a very inadequate description of a line of bulwarks from the Kerko Porta to the harbour. In the next place, more extensive fortifications were not required to protect the church, seeing it was well defended on the south by the acropolis on the western spur of the Sixth Hill. All that was necessary for the further security of the church was a wall on the west side of the plain on which it stood. Furthermore, the fortifications extending from the Kerko Porta to the foot of the Sixth Hill, commonly ascribed to Heraclius, have been proved to be the work of other hands, the greater part being the Wall of Manuel Comnenus,[[566]] while the remainder formed, originally, the defences of the Fourteenth Region.
The Wall of Leo the Armenian was erected in 813 to strengthen the defence of this part of the capital, in view of the preparations which the Bulgarians under Crum were making for a second attack upon Constantinople.[[567]] Crum had retired from his first assault upon the city, resolved not only to retrieve the defeat he had sustained, but also to punish the treacherous attempt upon his life, when he was proceeding to negotiate terms of peace with the emperor.
Arrangements had been made for holding a conference between the two sovereigns at a short distance to the west of the Heraclian Wall, on the explicit understanding that all persons present were to attend unarmed; so little confidence had the two parties in each other. But in flagrant breach of this agreement, Leo placed three bowmen in ambush near the place of meeting, with orders to shoot at the Bulgarian king, upon a preconcerted signal. In due time Crum arrived; but he had scarcely dismounted from his horse when his suspicions of a plot were aroused, and, springing into his saddle, he galloped back towards his camp. The arrows of the soldiers in ambush flew after him, wounding him although he escaped with his life.
The Byzantine historian who records the incident explains the failure of the plot as a Divine punishment upon the sins of his countrymen.[[568]] Crum saw the dastardly act in a different light, and, vowing vengeance, withdrew to Bulgaria to prepare for another war. He died before he could carry out his intention, but meanwhile Leo had put himself in readiness for the expected attack by constructing a new wall and a broad moat in front of the Wall of Heraclius.