After the battle of Kuyun Hissar (Baphaeon) we hear nothing of Osman until 1308. This year is memorable for several events of great importance. The first of these is the capture of Ak Hissar, the fortress guarding the place where the Sangarius finishes its descent and enters the plain behind Nicomedia. This was the last barrier opposing the progress of the Osmanlis through the narrow peninsula which stretches out between the Gulf of Nicomedia and the Black Sea to form the extreme north-western corner of Asia. Owing to the terrible misfortunes which had fallen upon the Byzantines through the Catalans, no effort seems to have been made to use Nicomedia as a base of operations for defending this peninsula. So before the year was out the Osmanlis appeared for the first time on the Bosphorus. In the years following the fall of Ak Hissar the Osmanlis slowly but thoroughly extended their authority until they were in possession of the harbours and fortresses of the Black Sea littoral between the mouth of the Sangarius and the Bosphorus. In the same year Kalolimni, an island of the Marmora, which lies near the mouth of the Gulf of Mudania, was occupied by Kara Ali.[76] By this the water-route from Brusa to Constantinople, and one of the two routes from Nicaea to Constantinople, were obstructed.[77] Kalolimni has the honour of being the first Ottoman island and the only one captured during the chieftainship of Osman. The investment of Brusa from the land side now began. So alarmed was the commandant that he sent Osman a ‘gift’ of money to purchase peace,[78] thus inaugurating the humiliating precedent which the mightiest emperors and kings of Christendom came in time to follow. It was in 1308, also, that Osman captured Tricocca,[79] which cut off the communication by land between Nicaea and Nicomedia. While he was engaged in dealing with Nicaea and Brusa, a danger threatened Osman from the east. A horde of Tartars was hovering along the confines of his state.[80] Some of them sacked Karadja Hissar at the time of the fair, and were prevented from marching on Eski Sheïr only by the timely arrival of Orkhan, who defeated them through the superiority of his cavalry. Instead of massacring his prisoners, Orkhan, as was the invariable custom of his father with the Greeks, offered the raiders Islam and Ottoman nationality.[81] It was in this way that the Osmanlis increased in numbers.