For the site of the Diplokionion, see Gyllius, _De Bosporo Thracio_, ii. c. 7. See also, Bondelmontius’ Map (the columns are more distinctly shown in the copy of that map found in Du Cange and Banduri, than in the copy which accompanies this work). The idea of Dr. Dethier, expressed in a note on Pusculus (_Siège de Constantinople_, p. 237), that the Diplokionion stood, in Byzantine days, at Cabatash, and was removed—columns and inhabitants together—to Beshiktash, after the Turkish Conquest, has no foundation whatever. Footnote 882: Page 753. Footnote 883: Dethier, _Siège de Constantinople_, No. xviii. p. 893. CHAPTER XVI. THE WALLS ALONG THE SEA OF MARMORA. The fortifications extending along the Sea of Marmora[883] from the Acropolis (Seraglio Point) to the southern extremity of the land walls consisted of a single wall flanked, according to Bondelmontius, by 188 towers—a line of defence some five miles in length. Almost everywhere along their course these fortifications stood close to the water’s edge, making it almost impossible to land troops at their foot, and giving them only the comparatively easy task of repelling an attack upon them with ships. [Illustration: Inscription in Honour Of Theodosius II. and the Prefect Constantine. (_See page 46._)] [Illustration: Inscription in Honour Of the Emperor Theophilus. (_See page 183._)] [Illustration: Inscription in Honour Of the Emperor Isaac Angelus. (_See page 132._)] What they had most reason to dread was the open sea upon whose margin they stood, its ceaseless, unwearied sap and mine of their foundations, and the furious assaults of its angry waves. This explains some peculiarities noticeable in their construction. The line of their course, for instance, was extremely irregular, turning in and out with every bend of the shore, to present always as short and sharp a front as possible to the waves that dashed against them. They were protected, moreover, by a breakwater of loose boulders,[884] scattered in the sea along their base. And the extent to which marble shafts were built, as bonds, into the lower courses of the walls and towers was, doubtless, another precaution adopted to maintain the stability of these fortifications. A large portion of these walls is built in arches closed on their outer face, and seems to be the work of a late age. The walls had at least thirteen entrances. The first gate, Top Kapoussi, a short distance to the south of the apex of the promontory, was known as the Gate of St. Barbara (ἡ τῆς μάρτυρος Βαρβάρας καλουμένη Πύλη),[885] after a church of that dedication in the vicinity; the presence of a sanctuary consecrated to the patroness of fire-arms at this point being explained by the fact that the Mangana, or great military arsenal of the city, stood a little to the south of the gate.