Achelous is the shape-changing god of the river Achelous, flowing southwards from the mountains of Thessaly with its mouth near Kalydon (see Calydonian boar hunt)
He is the longest river in Greece and compared by Herodotus to the Nile.
Story in short –
Achelous is mostly famous for wrestling Hercules for Denira and changing though a variety of shapes to defeat him, a snake, a hydra, a bull.
In the shape of bull he had one of his horns broken off. The horn went on to become the legendary horn of plenty
But Achelous himself never really recovered from his loss.
He appears in the Metamorphoses when, with his flooding waters and stories of floating trees and falling boulders, he captures Theseus returning from the boar hunt in Calydon. He gives the hero shelter and hospitality in his cave and they get to discussing whether the gods do or do not exist; each of them telling a series of stories to make their points and pass the time as they grow steadily more inebriated.
The stories they tell include
Baucis and Philemon
BACK – Calydon 
NEXT- Baucis and Philemon
Back to alphabetical
Bk VIII:547-610 Acheloüs tells Theseus and his friends of Perimele
Meanwhile, Theseus, having played his part in the united effort, turned back towards Athens, Tritonia’s city, where Erectheus once ruled. But the River Acheloüs, swollen with rain, blocked his immediate path, and stalled his journey. ‘Come under my roof, famous scion of Cecrops,’ the river-god said, ‘and do not commit yourself to my devouring waters. They are liable to carry solid tree-trunks along, in their roaring, and roll great boulders over on their sides. I have seen whole byres, near the bank, swept away, with all their livestock: and neither the cattle’s strength nor the horses’ speed was of any use. Many a strong man has been lost in the whirling vortices, when the torrent was loosed, after mountain snows. You will be safer to stay till my river runs in its normal channel, when its bed holds only a slender stream.’
Aegeus’s son nodded, and replied: ‘I will make use of your house, and your counsel, Acheloüs.’ And so he did. He entered the dark building, made of spongy pumice, and rough tufa. The floor was moist with soft moss, and the ceiling banded with freshwater mussel and oyster shells.
Now Hyperion, the sun, had measured out two thirds of his path of light, when Theseus and his companions of the hunt seated themselves on couches. Here was Pirithoüs, Ixion’s son, and there, Lelex, Troezen’s hero, his temples already streaked with thinning grey hair, and there were others whom the Acarnanian river-god, greatly delighted to have such a guest, judged worthy of equal honour. Quickly the barefoot nymphs set out dishes of food on the nearby tables, and when they had been cleared again, poured wine in jewelled cups. Then the greatest of heroes looking out over the waters below, asked: ‘What is that place?’ (He pointed with his finger.) ‘Tell me what name the island has, though it seems more than an island!’
The river-god replied ‘What you see is not one island: five pieces of land lie together, but the distance conceals their distinctiveness. This will make you less astonished at what Diana did to Calydon when she was slighted. Those islands were once nymphs, who, though they had slaughtered ten bullocks and invited the rural gods to the festival, forgot me as they led the festal dance. I swelled with anger, as fierce as when my flood is at its fullest, and terrible in wind and wave, I tore forest from forest and field from field, and swept the nymphs, who then, at last, remembered me, along with the place they trod, into the sea. There the ocean and my waters separated what had been continuous ground, and split it into as many parts as you see islands, the Echinades, there in the midst of the waves.
But as you can see for yourself, far off, far off one island vanishes, dear to me: the sailors call it Perimele. I loved her and stole her virginity. At which her father, unable to accept it, threw his daughter from the cliffs into the deep, intending to destroy her. I caught her, and holding her as she swam, I cried: ‘O God of the Trident, to whom rule over the restless waves, closest to earth, fell by lot, give your aid I beg, and grant a place to one whom a father’s anger drowns, or allow her to be that place herself!’ While I spoke, new earth clasped her body, as she swam, and a solid island rose, round her changed limbs.
https://www.poetryintranslation.com/PITBR/Latin/Metamorph8.php#Bkeight547
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