Themistocles now developed a second strategy. The route to southern Greece (Boeotia, Attica and the Peloponnesus) would require the army of Xerxes to travel through the very narrow pass of Thermopylae. This could easily be blocked by the Greek hoplites, despite the overwhelming numbers of Persians; furthermore, to prevent the Persians bypassing Thermopylae by sea, the Athenian and allied navies could block the straits of Artemisium. However, after the Tempe debacle, it was uncertain whether the Spartans would be willing to march out from the Peloponnesus again. To persuade the Spartans to defend Attica, Themistocles had to show them that the Athenians were willing to do everything necessary for the success of the alliance. In short, the entire Athenian fleet must be dispatched to Artemisium.