This great chief had more than one bosom-partner in his time ; but as we do not hear much of the institution of polygamy among the ancient Celts, it is to be hoped that he did not marry any one of them during the life of another. In his first years of fame, he found himself an object of general censure for indulging in the freedom of a single life, so he was forced by public opinion to change his state. But here arose an inconvenience. He could only ally himself to the family of one king or chief: consequently he would obtain the ill-will of many others. However, he showed himself equal to the occasion. He let it be generally understood that as his object in selecting a wife was the greater glory of the Fianna, in his be-, coming the father of future courageous, robust heroes, he would take his stand on a certain high hill in Munster on such a day, and he respectfully invited every lady who desired to be a mother of heroes to take her station at the base of the said hill, and at a given signal start for the summit, where he would be ready with open heart and arms to receive the fair competitor of healthy constitution and fleet limbs, who would first bless him with her presence. The invitation was not neglected. Many beauteous and active ladies sped upwards through rocks, grass, and heath at the signal, and, according to common report, Grainne, daughter of King Cormac, outstripped her rivals. As the nuptials of Fion and Grainne are differently related in one of the best of the Ossianic romances, we are inclined to think that Grainne's predecessor, the fair and fleet Maghneiss, was the successful aspirant on that day. However that may be, the hill thenceforward was called Sliabh na Bhan Fio?in (the Hill of the Fair Women), the Slienamon of the vulgar tongue.
In time the Lady Maghneiss died, and he obtained the hand of the daughter of King Cormac. This marriage was unfortunate for all parties. Grainne on her wedding-day laid geasa on Diarmuid to bear her away, and the flight and pursuit form the subject of the third volume of the Ossianic Transactions.