the sultan retreated despite the pleas of the Nicaean Turks. The rest of the crusaders arrived throughout the rest of May, with Robert Curthose (accompanied by Ralph de Guader) and Stephen of Blois arriving at the beginning of June. Meanwhile, Raymond and Adhemar built a large siege engine, which was rolled up to the Gonatas Tower in order to engage the defenders on the walls while miners mined the tower from below. The tower was damaged but no further progress was made. Byzantine arrival Byzantine emperor Alexios I chose not to accompany the crusaders, but marched out behind them and made his camp at nearby Pelecanum. From there, he sent boats, rolled over the land, to help the crusaders blockade Lake Ascanius, which had up to this point been used by the Turks to supply Nicaea with food. The boats arrived on 17 June, under the command of Manuel Boutoumites. The general Tatikios was also sent, with 2,000 foot soldiers. Alexios had instructed Boutoumites to secretly negotiate the surrender of the city without the crusaders' knowledge. Tatikios was instructed to join with the crusaders and make a direct assault on the walls, while Boutoumites would pretend to do the same to make it look as if the Byzantines had captured the city in battle. This was done, and on 19 June the Turks surrendered to Boutoumites. When the crusaders discovered what Alexios had done, they were quite angry, as they had hoped to plunder the city for money and supplies. Boutoumites, however, was named dux of Nicaea and forbade the crusaders from entering in groups larger than 10 men at a time. Boutoumites also expelled the Turkish generals, whom he considered just as untrustworthy. Kilij Arslan's family went to Constantinople and were eventually released without ransom. Alexios gave the crusaders money, horses, and other gifts, but the crusaders were not pleased with this, believing they could have had even more if they had captured Nicaea themselves. Boutoumites would not permit them to leave until they had all sworn an oath of vassalage to Alexios, if they had not yet done so in Constantinople. As he had in Constantinople, Tancred at first refused, but he eventually gave in. Aftermath The crusaders left Nicaea on 26 June in two contingents: Bohemond, Tancred, Robert II of Flanders, and Tatikios in the vanguard, and Godfrey, Baldwin of Boulogne, Stephen, and Hugh of Vermandois in