Blachernae is a suburb in the northeastern section of Constantinople. It was the site of a spring and a number of churches were built there, notably by Pulcheria in the 5th century and by Justinian I in the 6th century. These were originally outside the city walls, until 627 when the walls were expanded to include this section of the city. The area was expanded to include an imperial palace in the 11th century by Alexius I, but the walls were still relatively weak, reinforced only by the ramparts of the palace. After Alexius, the Blachernae Palace became the main residence of the emperors, though the old Great Palace was still used for major imperial ceremonies.
Its weakness was first exposed in the Fourth Crusade, when the invaders penetrated Blachernae. Blachernae was also the site of the St. Mary of Blachernae church, which became the second-most important church in Constantinople after Hagia Sophia, if only because the emperors' residence was nearby. In 1347, John VI Cantacuzenus was crowned there, instead of in Hagia Sophia. In 1453 during the Fall of Constantinople, Ottoman invaders attacked Blachernae with their large cannon, almost completely destroying the walls there; the Byzantine defenders failed to block the Kerkoporta gate, enabling the Turks to enter the city.
After the Ottoman conquest the sultan's residence was moved to Topkapi Palace on Acropolis Point, opposite to the original site of the Great Palace, which had by this time fallen into complete ruin, and the Blachernae area fell into disuse.