‘“Meanwhile the well-built ship speedily came to the isle of the two Sirens, for a fair and gentle wind bore her on. Then presently the wind ceased and there was a windless calm, and a god lulled the waves to sleep…the Sirens failed not to note the swift ship as it drew near, and they raised their clear-toned song: “‘Come hither, as thou farest, renowned Odysseus, great glory of the Achaeans; stay thy ship that thou mayest listen to the voice of us two.”’   Odyssey 12.181ff. (online text: Eng., Grk.)

Ancient Localizations

Strabo, Geography 1.2.12-13

“…or some of them assert that the Sirenes of Homer are situated close to Pelorus [Cape Pelorum], and others that they are more than two thousand stadia distant, near the Sirenussae, a three-peaked rock [Sorrento, which Strabo notes is not peaked and does not have three rocks, though it does have a sanctuary dedicated to the Sirens] which separates the Gulfs of Cummaea [Bay of Naples] and Posidonium [Gulf of Salerno] …while on the other side, looking towards the Gulf of Poseidonia, lie three uninhabited rocky little islands, called the Sirens [I Galli, the Galli rocks]… [Strabo discusses evidence, including a monument of Parthenope, one of the Sirens, in Naples] …we are more confident still that the position of the Sirenes was some where close by [Naples].”
(online text: Eng., Grk.)

Ptolemy, Geography 3.1

Ptolemy links the Sirenussae islands with the southwest coast of Italy

LI  GALLI  islands

(click to enlarge)