Beyond this the wall of Theodosius comes to an end abruptly. From this point the fortifications have a different character. "Along the greater portion of their course these bulwarks consisted of a single wall, without a moat; but at a short distance from the water, where they stand on level ground, they formed a double wall, which was at one time protected by a moat and constituted a citadel at the north-west angle of the city." They belong, Professor van Millingen has also clearly proved, to at least three periods, to the days of Heraclius, of Leo, and of Manuel Comnenus. After the Kerko-Porta the Theodosian walls turned eastwards; when the palace of Blachernae was defended it was probably by the erection, after the fifth century, of a new wall. The wall of Manuel Comnenus, built to give additional protection, left the earlier wall on an inner line of defence. The wall of Manuel is stronger than that of Theodosius, but it has no moat; it resisted all the efforts of the Turkish artillery in 1453. The public gate in it was that of the Kaligaria (the district where military shoes were made), and from a tower beside it the last Emperor and Phrantzes reconnoitred early in the morning of the last day of the siege. North of this, from the tower which stands at the point where the wall turns eastwards, the fortifications seem to have been entirely rebuilt during the repairs of the fourteenth and fifteenth century. In this piece stands the gate of Gyrolimnè, through which probably the leaders of the Crusaders in 1203, who were encamped on the hill just outside, entered to negotiate with Isaac Angelus. Behind it stood the palace of Blachernae, the site of which may be expected to reveal much when it is excavated. Beyond this, from the great tower, unbattlemented, which has on it an inscription in honour of Isaac Angelus, who reconstructed it in 1188, the greatest difficulties surround the identification of the different portions. The first part of the wall is of great height--sometimes sixty-eight feet--and of thickness varying from over thirty to over sixty feet. Three towers protect this part: two "twin towers" rising to a great height above the walls. The special character of the walls is determined by the fact that, within, the palace of Blachernae stood upon a terraced hill. The second tower, much higher than that with the inscription, may be identified with the tower of Isaac Angelus, described by Nicetas Choniates as built by the Emperor both for the defence of Blachernae, and for a residence for himself. Beyond it is a third tower, which has been generally considered to be the tower of Anemas, mentioned first by Anna Comnena, as the place in which Anemas, who had conspired against her father, was confined.