The river-god Achelous told the story of Erisichthon to Theseus and his companions, whom he was entertaining at his hospitable board, while they were delayed on their journey by the overflow of his waters. Having finished his story, he added, "But why should I tell of other persons' transformations when I myself am an instance of the possession of this power? Sometimes I become a serpent, and sometimes a bull, with horns on my head. Or I should say I once could do so; but now I have but one horn, having lost one." And here he groaned and was silent.
Theseus asked him the cause of his grief, and how he lost his horn. To which question the river-god replied as follows: "Who likes to tell of his defeats? Yet I will not hesitate to relate mine, comforting myself with the thought of the greatness of my conqueror, for it was Hercules. Perhaps you have heard of the fame of Dejanira, the fairest of maidens, whom a host of suitors strove to win. Hercules and myself were of the number, and the rest yielded to us two. He urged in his behalf his descent from Jove and his labors by which he had exceeded the exactions of Juno, his stepmother. I, on the other hand, said to the father of the maiden, 'Behold me, the king of the waters that flow through your land. I am no stranger from a foreign shore, but belong to the country, a part of your realm. Let it not stand in my way that royal Juno owes me no enmity nor punishes me with heavy tasks. As for this man, who boasts himself the son of Jove, it is either a false pretence, or disgraceful to him if true, for it cannot be true except by his mother's shame.' As I said this Hercules scowled upon me, and with difficulty restrained his rage. 'My hand will answer better than my tongue,' said he. 'I yield to you the victory in words, but trust my cause to the strife of deeds.' With that he advanced towards me, and I was ashamed, after what I had said, to yield. I threw off my green vesture and presented myself for the struggle. He tried to throw me, now attacking my head, now my body. My bulk was my protection, and he assailed me in vain. For a time we stopped, then returned to the conflict. We each kept our position, determined not to yield, foot to foot, I bending over him, clenching his hand in mine, with my forehead almost touching his. Thrice Hercules tried to throw me off, and the fourth time he succeeded, brought me to the ground, and himself upon my back. I tell you the truth, it was as if a mountain had fallen on me. I struggled to get my arms at liberty, panting and reeking with perspiration. He gave me no chance to recover, but seized my throat. My knees were on the earth and my mouth in the dust.
"Finding that I was no match for him in the warrior's art, I resorted to others and glided away in the form of a serpent. I curled my body in a coil and hissed at him with my forked tongue. He smiled scornfully at this, and said, 'It was the labor of my infancy to conquer snakes.' So saying he clasped my neck with his hands. I was almost choked, and struggled to get my neck out of his grasp. Vanquished in this form, I tried what alone remained to me and assumed the form of a bull. He grasped my neck with his arm, and dragging my head down to the ground, overthrew me on the sand. Nor was this enough. His ruthless hand rent my horn from my head. The Naiades took it, consecrated it, and filled it with fragrant flowers. Plenty adopted my horn and made it her own, and called it 'Cornucopia.'"
The ancients were fond of finding a hidden meaning in their mythological tales. They explain this fight of Achelous with Hercules by saying Achelous was a river that in seasons of rain overflowed its banks. When the fable says that Achelous loved Dejanira, and sought a union with her, the meaning is that the river in its windings flowed through part of Dejanira's kingdom. It was said to take the form of a snake because of its winding, and of a bull because it made a brawling or roaring in its course. When the river swelled, it made itself another channel. Thus its head was horned. Hercules prevented the return of these periodical overflows by embankments and canals; and therefore he was said to have vanquished the river-god and cut off his horn. Finally, the lands formerly subject to overflow, but now redeemed, became very fertile, and this is meant by the horn of plenty.
There is another account of the origin of the Cornucopia. Jupiter at his birth was committed by his mother Rhea to the care of the daughters of Melisseus, a Cretan king. They fed the infant deity with the milk of the goat Amalthea. Jupiter broke off one of the horns of the goat and gave it to his nurses, and endowed it with the wonderful power of becoming filled with whatever the possessor might wish.
The name of Amalthea is also given by some writers to the mother of Bacchus. It is thus used by Milton, "Paradise Lost," Book IV.:
"... That Nyseian isle,
Girt with the river Triton, where old Cham, Whom Gentiles Ammon call, and Libyan Jove, Hid Amalthea and her florid son, Young Bacchus, from his stepdame Rhea's eye."