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Altar of the Twelve Gods Near the middle of the open square, somewhat to the north, lay the Altar of the Twelve Gods (Fig. 7), today largely hidden under the Athens–Piraeus railway (1891). A corner of ... The altar was one of the few monuments permitted within the open square and it served as the zero milestone or center of the city. ... On a milestone dating to ca. 400 B.C. we read: "The city set me up, a truthful monument to show all mortals the measure of their journeying: the distance to the altar of the twelve gods from the harbor is forty-five stades" (IG II2 2640).