The Moscovite mentions an encounter during this attack between a Greek strategos or general named Rangebè and a Turk named Amer Bey, the standard-bearer of the sultan. The Greek made a sortie, put the followers of Amer to flight, and then attacked Amer himself, whom he cut in two. The Turks, furious at the loss, surrounded Rangebè and killed him.[335] The next day the Venetian Council of Twelve decided that Trevisano with his four hundred men should leave the entrance to the harbour and take up the defence of the newly threatened walls at Aivan Serai. There appears, however, to have been considerable opposition on the part of his crews, who preferred to remain afloat. Finally this was overcome, and on the 13th they went to their positions at the place mentioned, where the defenders had been occupied in constantly repairing the breaches made by the guns. Trevisano’s galleys were left in the imperial harbour of Neorion near the end of the chain. His place was taken by Diedo, captain of the Tana galleys, who was now appointed to the chief command of the fleet. [Sidenote: A new assault on May 12.] At midnight of the 12th fifty thousand Turks made an attack near Tekfour Serai, the Palace of the Porphyrogenitus, between Adrianople Gate and Caligaria, where a battery of guns had been planted from the commencement of the siege and had greatly damaged the breastwork and the Outer Wall. The attack was made with such force, and the shouting of the invaders was so loud, that Barbaro says ‘most of us believed that they would capture the city.’ Once more the attack failed. On the 14th, Mahomet removed the guns which he had placed on the slope of Pera Hill and had them taken to Aivan Serai and placed so as to attack the gate of the imperial palace of Blachern. It was found, however, that the guns in this position did no great harm, and they were once more removed, taken to the Lycus valley, and placed near the others to batter the walls near the Romanus Gate. From this time onward this was the principal place against which Mahomet concentrated his attack. The entries in the diaries of the siege, showing that, while other parts of the wall were often attacked, the bombardment in the Lycus valley was unceasing day and night, occur during many days with monotonous regularity. Equally constant were the efforts for the defence: ‘We, on our side, were working day and night to repair the walls with logs and earth and other materials.’ [Sidenote: New attempts to force the boom, on May 16 and 17.]