To the west of the Bucoleon is the beautiful Church of SS. Sergius and Bacchus, erected by Justinian the Great; for some account of which the reader is referred to the chapters on the churches of the city. The district extending thence to the ancient Gate of S. Æmilianus (Daoud Pasha Kapoussi) is remarkable for having been occupied by the artificial harbours, constructed, from time to time, on the southern side of the city in the interest of commerce, or for the use of the imperial navy. They were four in number, and, notwithstanding the changes of centuries, they have left their impress upon the ground to a degree which allows their site and contour to be clearly identified. First in the order of position, though not of time, came the Harbour of the Emperor Julian, below the Hippodrome. It has already been noticed in the history of the making of Constantinople. It was used for some time even after the Turkish Conquest, but was ultimately abandoned for the deeper water found along the shores of the Golden Horn. The Harbour of the Kontoscalion followed; in the quarter which the Greek population still designates by that old name, but which is commonly known as Koum Kapoussi. It has been filled in, but the mole remains, as well as a considerable portion of the wall around the basin of the harbour. The entrance could be closed against an enemy by great gates of iron bars, and in bad weather three hundred galleys, of fifty or a hundred pairs of oars, might be seen taking refuge here, waiting for a favourable wind. Next in order was the Harbour of Kaisarius, known also as the Neorion or Dockyard of the Heptascalon, which stood where the Turkish quarter of Tulbenkdji Djamissi is now situated. But few traces of it are left. Indeed its position had been forgotten, and its distinctness from the other harbours along this shore ignored, until 1819, when a great fire in the district revealed the fact that the quarter of Tulbenkdji Djamissi stood in the basin of an old harbour, enclosed by a wall built in three tiers of huge blocks. This agreed with other indications of the presence of a harbour at this point hitherto left unexplained--a mole in front of the shore of the quarter, and a gap in the mole forming an entrance to which corresponded an old opening in the city walls, now closed by masonry of Turkish construction. It harmonised also with the description which the historian Pachymeres gives of a harbour constructed or restored by the Emperor Michael Palæologus on this side of the city. Here Phocas placed troops to oppose the landing of Heraclius, and here also the Emperor Constantine Pogonatus, in 673, stationed his ships, armed with Greek fire, to await the fleet of the Saracens in the first siege of Constantinople by that formidable foe.