According to Herodotus, the Athenians insist that their compatriots must send their fleets to Salamis, a small island just opposite the Athenian harbors. The Athenians act like this, because they do not trust the Spartans, who had promised to send an army to Boeotia to defend Athens, but were actually building a wall across the Corinthian isthmus and destroying the road leading to the isthmus, which is usually called Skiron's road (picture below).
Skiron's road can be found a little west of Megara, a town between Athens and Corinth. At the moment, there are two roads, but one can easily imagine that this was a very narrow path in Antiquity. Remains of the wall across the Corinthian isthmus can still be seen a little south of the sanctuary of the Isthmian Poseidon. It is very likely that the Persian cavalry reached this wall, because Pausanias (a Greek author from the second century CE who had read many ancient texts) mentions that the Persians fired arrows at one of the Corinthian harbors, and archaeologists have discovered that the temple of Poseidon was destroyed by fire during the Persian Wars.
According to the inhabitants of Megara, Skiron was a friendly hero who built a road to Corinth through the steep rocks along the sea. The Athenians, who were often on bad terms with the Megarians, put the story upside down: in the legend of their hero Theseus, Skiron was an evil man who asked his guests to wash his feet, and when they were stooped down, kicked them from the cliffs into the sea, where a giant man-eating turtle finished the killing. According to the Athenian story, Theseus eventually killed Skiron.