Mohammed then embarked on a new scheme. It had been done before but never on such a scale against such formidable obstacles. It was ironic that on April 21st, while Mohammed was absent from the camp planning his new stratagem, the ceaseless cannonading suddenly brought down the Bactatinian tower along with a large portion of the adjoining Outer Wall. The city's defenses had been breached. The defenders saw they were now virtually defenseless against a determined Turkish attack. Yet no attack came. There was no one in the camp with the authority to give the order. That night the Greeks hastily patched up the gap with a parapet of earth and rubble topped with a palisade and barrels filled with earth.

Mohammed was at the Turkish naval base of the Double Columns. There were thousands of workmen engaged in his secret project. Meanwhile several batteries of guns were positioned along the headlands of the Golden Horn.

Shortly after dawn on April 22nd the sentinels on the walls gazed across the Golden Horn and beyond Galata and gasped at the outlandish sight of a line of Turkish ships, sails hoisted and billowing in the breeze, sailing across the hills behind the Genoese town.

It was a stupendous engineering feat. Some seventy ships, including even a few triremes and biremes weighing well over a hundred tons, were being hauled from the Bosphorus by straining oxen and men up a slope of two hundred feet; then they were fitted onto cradles on a roadway of planks greased with fats and dragged a mile over hills that rose to 350 test above sea level, finally to slither into the waters of the Golden Horn. The boom had been outflanked.

Twice in the past fleets had been dragged six miles over the isthmus of Corinth, once by Augustus after the battle of Actium and once by a Greek general in the 10th Century; the Syracusan fleet of Dionysius I had been transported nearly three miles over the isthmus of Motya, and Hannibal had once done the same to introduce his fleet into the harbor of Tarentum; but in all these cases the land had been relatively flat.

This was the most serious threat to the city to date. There was not an inhabitant who did not remember the chilling tales of crusaders. Constantine hastily summoned a council of war. There was dissatisfaction with the Genoese because no one in Galata had warned the city about the Sultan's preparations. Thus only Venetians were invited to the council, with the exception of Giustiniani. After much discussion a plan was devised to attack the Turkish ships. Secret preparations were begun immediately. The attack was planned for the night of April 24.

Meanwhile, on the 23rd, Constantine sent an emissary to the Sultan offering peace and the payment of a large tribute. This offer Mohammed rejected. He insisted the city should surrender unconditionally. He would then personally guarantee the safety of the citizens. It was not an offer that appealed to the defenders. They were still confident they could hold out, and no one trusted the young Mohammed to keep his promises.

The secret preparations for the naval attack became known to the Genoese. They were furious they had been excluded and demanded to be allowed to take part. Constantine had to finally agree to this. But as the Genoese had no ship ready, the attack had to be rescheduled for April 28th.

This delay was fatal. Mohammed's spies in Galata eventually learned of the plan. Two hours before dawn on the 28th, the attack party silently slipped out of harbor into the Golden Horn. Leading the flotilla were two large transports with their sides protected against cannon fire by bales of wool. Following these were two Venetian war galleys each with forty rowers. Inside the protective square formed by these four vessels were three fustae long-boats, each with seventy oarsmen, and a number of smaller craft loaded with combustible materials. The plan was to creep up on the Turkish fleet moored at the head of the Golden Horn, and during the attack the small craft would slip unnoticed into the midst of the Turks and set their ships aflame.

But the Turks were waiting. They had even added more batteries to the guns on the headlands protecting their fleet. In the two-hour battle one Venetian galley and several of the small craft were sunk. The Greeks retired after destroying only one enemy ship. The Turks captured forty Christian sailors. Later that day these unfortunate men were brought before the walls and slaughtered. In retaliation Constantine ordered 260 Turkish prisoners brought up to the battlements where there in the sight of the Turks they were beheaded.