These new foes of the empire deserve a word of description. Othman, the son of Ertogrul, was a vassal of the Seljouk Sultan of Roum, who had been granted a tract in the Phrygian highlands under the condition of military service against the Greeks. His fief lay in the north-west angle of the great central plateau of Asia Minor. Behind it lay the rolling country of hills and uplands already occupied by the Seljouks. Before it were the Bithynian mountains, with their passes protected by forts, and garrisoned by local militia, till the day when they were so perversely stripped of their defenders by the action of Michael Paleologus. Othman, and his father Ertogrul before him, owned nothing in the hills, nor could they have pushed on if Michael had not made the way easy for them. But after 1270 the native militia was gone, and the followers of Othman, instead of having to face an armed population, fighting to protect its own fields, found to oppose them only inadequate garrisons of regular troops at long intervals. Othman’s life covered two series of great events, the disastrous reign of Andronicus II. at Constantinople, and in Asia Minor the no less disastrous break-up of the power of his own suzerain, the Sultan of Roum. In 1294, Gaiaseddin, the last undisputed sovereign of the Seljouk line, fell in battle against rebels; and in 1307, Alaeddin III., the last prince who claimed to be supreme Sultan, died in exile. This made Othman an independent prince; but he did not take the title of Sultan, contenting himself with the humbler name of Emir. Othman’s field of operation from 1281 to 1326 was the Byzantine borderland of Bithynia and Mysia. He was by no means the strongest of the Seljouk chiefs who made a lodgement within the borders of the empire, and it took him twenty years before he conquered one large town. His wild horsemen harried the open sea-coast plain of Bithynia again and again, till at last the wretched inhabitants emigrated, or acknowledged him as their sovereign. But the towns, within their strong Roman walls, were unassailable by the light cavalry which formed his only armed strength. The siege of Prusa [Broussa], the capital and key of the region, lasted ten years. The Turks built a chain of forts around it and gradually made the introduction of provisions more and more difficult, till at last a large force was required to march out every time that a convoy was expected. At length the inhabitants could find no advantage in spending their whole lives in a beleaguered town undergoing slow starvation. Prusa surrendered in 1326, and Othman heard of the news on his death-bed. The Turkish frontier now once again touched the Sea of Marmora, which it had not reached since the Crusaders thrust it back inland in 1097.