Plutarch, Theseus
Bernadotte Perrin, Ed.

And after the Median wars, in the Archonship of Phaedo,¹ when the Athenians were consulting the oracle at Delphi, they were told by the Pythian priestess to take up the bones of Theseus, give them honorable burial at Athens, and guard them there. But it was difficult to find the grave and take up the bones, because of the inhospitable and savage nature of the Dolopians, who then inhabited the island. However, Cimon took the island, as I have related in his Life,² and being ambitious to discover the grave of Theseus, saw an eagle in a place where there was the semblance of a mound, pecking, as they say, and tearing up the ground with his talons. By some divine ordering he comprehended the meaning of this and dug there, [2] and there was found a coffin of a man of extraordinary size, a bronze spear lying by its side, and a sword. When these relics were brought home on his trireme by Cimon, the Athenians were delighted, and received them with splendid processions and sacrifices, as though Theseus himself were returning to his city. And now he lies buried in the heart of the city, near the present gymnasium,³ and his tomb is a sanctuary and place of refuge for runaway slaves and all men of low estate who are afraid of men in power, since Theseus was a champion and helper of such during his life, and graciously received the supplications of the poor and needy. [3] The chief sacrifice which the Athenians make in his honor comes on the eighth day of the month Pyanepsion, the day on which he came back from Crete with the youths. But they honor him also on the eighth day of the other months, either because he came to Athens in the first place, from Troezen, on the eighth day of the month Hecatombaeon, as Diodorus the Topographer states, or because they consider this number more appropriate for him than any other since he was said to be a son of Poseidon.⁴ [4] For they pay honors to Poseidon on the eighth day of every month. The number eight, as the first cube of an even number and the double of the first square, fitly represents the steadfast and immovable power of this god, to whom we give the epithets of Securer and Earth-stayer.