The Aeneid by Virgil Book 6 Page 21

Here on a sudden, in trembling terror, Aeneas grasps his sword, and turns the naked edge against their coming; and did not his wise companion warn him that these were but faint, bodiless lives, flitting under a hollow semblance of form, he would rush upon them and vainly cleave shadows with steel.

From here a road leads to the waters of Tartarean Acheron. Here, thick with mire and of fathomless flood, a whirlpool seethes and belches into Cocytus all its sand. A grim ferry man guards these waters and streams, terrible in his squalor – Charon, on whose chin lies a mass of unkempt hoary hair; his eyes are staring orbs of flame; his squalid garb hangs by a knot from his shoulders. Unaided, he poles the boat, tends the sails, and in his murky craft convoys the dead – now aged, but a god’s old age is hardy and green.