defences had been originally constructed on a magnificent scale and with
great skill, according to the ancient art of war. Even though they were
partly ruined by time and weakened by careless reparations, they still
offered a formidable obstacle to the imperfect science of the engineers
in Mahomet's army. Two lines of wall, each flanked with its own towers,
rose one above the other, overlooking a broad and deep ditch. The
interval between these walls enabled the defenders to form in perfect
security, and facilitated their operations in clearing the ditch and
retarding the preparation for assault. The actual appearance of the low
walls of Constantinople, with the ditch more than half filled up, gives
only an incorrect picture of their former state.

Mahomet had made his preparations for the siege with so much skill that
his preliminary works advanced with unexpected rapidity. The numerical
superiority of his army, and the precautions he had adopted for
strengthening his lines, rendered the sorties of the garrison useless.
The ultimate success of the defence depended on the arrival of assistance
from abroad; but the numbers of the Ottoman fleet seemed to render even
this hope almost desperate. An incident occurred that showed the
immense advantage conferred by skill, when united with courage, over an
apparently irresistible superiority of force in naval warfare. Four large
ships, laden with grain and stores, one of which bore the Greek and the
other the Genoese flag, had remained for some time wind-bound at Chios,
and were anxiously expected at Constantinople. At daybreak these ships
were perceived by the Turkish watchmen steering for Constantinople, with
a strong breeze in their favor. The war-galleys of the Sultan immediately
got under way to capture them. The Sultan himself rode down to the point
of Tophane to witness a triumph which he considered certain and which he
thought would reduce his enemy to despair. The Greeks crowded the walls
of the city, offering up prayers for their friends and trembling for