DIOMEDEAE INSULAE(αἱ Διομήδειαι νῆσοι), a group of small islands off the coast of Apulia. now called ISOLE DI TREMITI:they are distant about 15 miles from the nearest point of the coast, and 18 from the mouth of the river Frento ( Fortore). Their ancient name was derived from the legend which represented them as the scene of the transformation of the companions of Diomed into birds; a species of large sea-fowl by which they were inhabited (called by Pliny Cataractes—apparently a kind of diver) were supposed to be the descendants of these Greek sailors, and were said to display a marked partiality for all visitors of Hellenic extraction. (Strab. 6. p. 284; Lycophr. Alex. 594—609; Pseud-Arist. de Mirab. § 79; Anton. Lib.; Steph. B. s. v.;Ovid, Ov. Met. 14.482—509; Plin. Nat. 10.44. s. 61; Ael. H.A. 1.1; Dionys. Per. 483.) Ancient authors differ considerably in regard to their number. Stephanus, Lycophron, and the mythographers, as well as Aelian and Dionysius, mention only one island, which they call Διομήδεια νῆσος;Strabo says there are two, one of which is inhabited, the other not; Pliny (Plin. Nat. 3.26. s. 30) calls the larger island Diomedia insula,and adds that there is another of the same name, but called by some Teutria; Ptolemy (Ptol. 3.1.80) says there are five, but without giving their names. The real number is three islands, besides some mere rocks; they are now called S. Domenico, S. Nicola, and Caprara:these three lie close together, while the small island of Pianosa(distant 11 geog. miles to the NE.) is not now reckoned to belong to the group, but may perhaps be the Teutria of Pliny. The island of S. Domenicois much the largest of the three, and is evidently the Diomedia Insula of the ancients, where a shrine of that hero and his tomb were shown, together with a grove of plane trees, said to be the first introduced into Italy. (Plin. Nat. 12.3.) But the same island was also known by the name of TRIMERUS,probably its vernacular or native name, from whence comes the modern appellation of Tremiti, now applied to the whole group. We learn from Tacitus that Augustus selected it for the place of exile of his daughter Julia. (Tac. Ann. 4.71.) The name is already written Tremetisby the Geographer of Ravenna in the 9th century. (Anon. Ravenn. 5.25, ed. Gronov.)
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