OSISMI or OSISMII(Ὀσίσμιοι), a Celtic people who joined the Veneti in the war against Caesar, B.C. 56. ( B. G. 3.9.); There is nothing in Caesar which shows their position further than this, that they were in the peninsula of Bretagne. Ptolemy (Ptol. 2.8.5) makes them extend as far south as the Gobaeum headland, and lie names Vorganium as their chief city. [GOBAEUM] If we accept the authority of Mela, who says (3.6) that the island Sena (Sein) is opposite to the shores of the Osismii, this will help us to determine the southern limit of the Osismii, and will confirm the conjecture of Gobaeum being the headland called Raz Pointe, which is opposite to the small island Sein, or as it is improperly called Isle des Saints;or being somewhere near that headland. In another passage (3.2). Mela makes the great bend of the west coast of Gallia commence where the limits of the Osismii end: ab illis enim iterum ad septentriones frons littorum respicit, pertinetque ad ultimos Gallicarum gentium Morinos.Pliny (Plin. Nat. 4.18) describes this great peninsula of Bretagnethus: Gallia Lugdunensis contains a considerable peninsula, which runs out into the ocean with a circuit of 625 miles, beginning from the border of the Osismii, the neck being 125 miles in width: south of it are the Nannetes.It is plain then that Pliny placed the Osismii along the north coast of Bretagne, and there is Mela's authority for placing them on the west coast of the peninsula. The. neck of the peninsula which Pliny describes,, may be determined by a line drawn from the bay of St. Brieucon the north to Lorienton the south, or rather to some of the bays east of it, or Morbihan. It seems a fair conclusion, that the Osismii occupied a large part of the peninsula of Bretagne;or as Strabo (4. p. 195) says: Next to the Veneti are the Osismii, whom Pytheas calls Timii, who dwell in a peninsula which runs out considerably into the ocean, but not so far as Pytheas says and those who believe him.He does not tell us how far Pytheas said that the peninsula. ran out into the sea, but if we had Pytheas' words, we might find that he knew something about it. The conclusion of D'Anville is justified by the ancient authorities. He says: It seems that it has been agreed up to the present time to limit the territory of the Osismii to the northern coast of Basse Bretagne, though there are the strongest reasons for thinking. that they occupied the extremity of the same continent in all its breadth and that the diocese of Quimperwas a part of the territory as well as the diocese of Léon. D'Anville observes that there is no part of ancient Gaul the geography of which is more obscure.
[G.L]