The Aeneid by Virgil Book 3 Page 30

the circuit be; shun the shore and waters on the right. These lands, they say, of old broke asunder, torn by force of mighty upheaval – such vast change can length of time effect – when the two countries were one unbroken whole. The sea came in force between, cut off with its waters the Hesperian from the Sicilian coast, and with narrow tideway washes fields and cities on severed shores. Scylla guards the right side; insatiate Charybdis the left; and at the bottom of her seething chasm thrice she sucks the vast waves into the abyss, and again in turn throws them upwards, lashing the stars with spray.

But Scylla a cavern confines in dark recesses, from which she thrusts forth her mouths and draws ships on to her rocks. Above she is of human form, down the waist a fair-bosomed maiden; below, she is a sea dragon