Pausanias Description of Greece 1.28.10

[10] At the Delphinion are tried those who claim that they have committed justifiable homicide, which was the plea put forward by Theseus on the occasion when he was acquitted, after having killed Pallas, who had risen in revolt against him, and his sons. Before Theseus was acquitted it was the established custom among all men for the one who sheds blood to go into exile, or, if he remained, to be put to a similar death. The Court in the Prytaneion [‘City Hall’], as it is called, where they try iron and all similar inanimate things, had its origin, I think [ nomizō], in-response-to [ epi + dative case] the following event. It was when Erekhtheus was king of Athens that the ox-slayer [ bou-phonos] first killed an ox at the altar [ bōmos] of Zeus Polieus. Leaving the axe [ pelekus] where it lay he went out of the land into exile, and the axe [ pelekus] was immediately put-on-trial [ krinesthai] and acquitted, and the trial has been repeated year by year down to the present.