Sunium was situated on a high point of land at the southern tip of Attica, the Greek peninsula upon which Athens is the most prominent city. It was at Sunium that the Persians destroyed a partially completed Greek temple. The Greeks committed themselves to build another and erected a beautiful marble structure which they dedicated to the sea god, Poseidon. Given that Sunium jutted into the sea, it was only appropriate that they paid special attention to this watery deity.

Geographically, Sunium was about twenty-five miles southeast of Athens. Given this distance, it would have take one day, two at most, for the ship from Delos to reach the city. As Socrates is to be executed the day after its return, it is speculation whether he will die on the second or the third day.