The wood of the white poplar tree is the only wood that the people of Elis employ in the sacrifices of Zeus, giving that tree this especial honour, I imagine, because Hercules introduced it from Thesprotia into Greece. And I think there can be little doubt that Hercules himself, when he sacrificed to Zeus at Olympia, burnt the thighs of the victims on white poplar wood. Hercules found this tree growing near the Acheron a river in Thesprotia, and that is why they say it is called Acherois by Homer.[71] In all ages rivers have been celebrated for the growth of various grasses and trees on their banks. Thus the Mæander is most famous for tamarisks, and the Asopus in Bœotia for immense reeds, and the Persea is found only on the banks of the Nile. Thus there is no wonder that by the Acheron first grew the white poplar, and that the wild olive grows near the Alpheus, and that the black poplar grows on Celtic soil by the river Eridanus. Let us now, as we have made mention of the greatest altar, enumerate all the altars at Olympia. I will take them in the order the people of Elis are accustomed to sacrifice at them. They first sacrifice to Vesta, and next to Olympian Zeus in the altar inside the temple, thirdly to Hermes, fourthly to Artemis, fifthly to Athene the Goddess of Booty, sixthly to Athene Ergane. To this Athene the descendants of Phidias, (called the cleansers because they received from the people of Elis the honour of cleansing the statue of Zeus from anything clinging to it), sacrifice before they commence polishing up the statue. And there is also another altar of Athene near the temple, and near it a square altar of Artemis tapering up gradually at the top. And next to those we have mentioned they sacrifice to Alpheus and Artemis at one altar: the reason for this I learnt from one of Pindar’s Odes, and I have recorded it in my account of the Letrinæans.[72] And at no great distance from this is another altar to Alpheus, and near it an altar to Hephæstus, which some of the people of Elis say is the altar of Martial Zeus, at which Œnomaus sacrificed when he proposed the horse-race for the suitors of his daughter Hippodamia. Next is an altar of Hercules under the title of Aider, and altars to Hercules’ brothers, Epimedes and Idas and Pæonæus and Iasus. I know that the altar of Idas is called the altar of Acesidas by some. And at the ruins of the house of Œnomaus are two altars, one of Household Zeus, built apparently by Œnomaus, the other built afterwards I think to Zeus of the Lightning, when lightning had struck the house. With reference to the great altar, called the altar of Olympian Zeus, I have already spoken a little above. And near it is the altar to Unknown Gods, and next that of Zeus the Cleanser, and Victory, and next that of Zeus Chthonius. There are also altars of all the gods, and one of Olympian Hera also made of _débris_, the votive offering they say of Clymenus. And next to it is a joint altar