On the Marmora the walls were to be watched by the fleet under Baltoglu from the southern end of the landward walls, round the present Seraglio Point as far as Neorion, which was near the end of the boom. The main object of the fleet was, however, to force an entry into the harbour, and for this purpose to capture or destroy the ships at the boom, an object which Baltoglu attempted to attain from the very commencement of the siege.[254] The city was thus under attack on two sides, the third--namely, that looking over the Golden Horn--protected by the boom, was for the present inaccessible to the Turkish fleet. The difficulty of determining the number and disposition of Mahomet’s cannon opposite the landward walls arises from the fact that the position of several of them was changed and that their numbers possibly varied. Phrantzes mentions fourteen batteries along the length of the wall, each containing four guns. Barbaro speaks of nine batteries. Montaldo says that the Turks had in all two hundred guns or ‘torments.’[255] Each of the nine batteries was strengthened by the addition of a heavy gun. Critobulus represents Mahomet as stating after his guns had done their work that he had opened a way into the city at three places, and this declaration affords a safe guide to the general disposition of the cannon. These were, first, between the present Tekfour Serai and the Adrianople Gate; second, opposite or near the Pempton or Gate of the Assault (usually spoken of by contemporaries as the Romanus Gate[256]) in the Lycus valley, and the last near the Third Military Gate between the Pegè or Silivria Gate, and the Rhegium Gate, now called Mevlevihana Capou. Here were the three principal stations of Mahomet’s cannon. At these three places the ruined condition of the wall bears testimony to the vigorous attack of cannon. At them and nowhere else is it possible to pass over the foss, the breastwork and Outer Wall, and to see that the Inner Wall has been so broken down that a passage into the city was possible.[257] Three cannon are especially remembered on account of their great size. According to Leonard, the largest--that, namely, cast by Urban, which threw a ball of twelve hundred pounds weight--was first placed at Caligaria[258] which then, as now, was ‘protected neither by a foss nor by a front wall.’ It was destroyed either by the besieged or through an accident by which Urban was killed, after it had done considerable damage to the walls.[259] It was, however, recast and transferred to the Lycus valley, where it demolished the Bactatinean tower.[260] The statement of Chalcondylas is that of these three large guns one was stationed opposite the Imperial Palace, probably at Caligaria, the second opposite the Romanus Gate, where the sultan had fixed his camp, and the third between them.[261] The largest and most powerful gun remained during the siege at the Mesoteichion, in front of the imperial tent.[262]