It is surprising that an idea apparently so central to Greek religion as the twelve gods or Dodekatheon can be traced back no further than the late sixth century BC. This is when an altar of the twelve gods was set up in the agora at Athens by the archon Peisistratos, son of Hippias, and grandson of Peisistratos the tyrant, in 522 BC, during the regime of Hippias. It was a modest, square structure, situated in the northwest corner of the agora, discovered during the construction of the Athens–Piraeus railway, and now bisected by it. The altar of the twelve gods was the symbolic centre of the city: in one of his Dithyrambs for Athens (fr. 75) Pindar calls on the gods who come to the ‘incense-rich navel in holy Athens and the glorious, richly adorned agora’, on the occasion of the ritual reception of Dionysos there at the Dionysia festival. The striking word ‘navel’ (ὀμφαλός) suggests Delphi, the navel-stone and exact centre of the earth, where two eagles let go from the East and the West met. Distance was measured from the Athenian altar: Herodotus (2.71.1) points out that the distance from the city of Heliopolis in Egypt to the Mediterranean Sea was almost exactly the same as that from the altar of the twelve to Olympia. A verse inscription from the fifth century specifies the distance from the altar of the twelve to the Peiraeus. One gets a glimpse of a well-organized measuring system.