Battle of Crocus Field
The Third Sacred War (often just called 'the' Sacred War) broke out in 356 BC, and would present Philip with his first real opportunity to expand his influence into the affairs of central and southern Greece. The war was caused by the refusal of the Phocian Confederation to pay a fine imposed on them in 357 BC by the Amphictyonic League, a pan-Greek religious organisation which governed the most sacred site in Ancient Greece, the Temple of Apollo at Delphi. Behind the religious element, there probably lay a display of "realpolitik" in bringing charges against the Phocians, instigated by the Thebans. At this time, Thebes controlled a majority of the votes in the council, and at the autumn meeting in 357 BC, the Thebans were able to have both the Phocians (for the cultivation of the sacred land) and the Spartans (for occupying Thebes some 25 years previously) denounced and fined. Since the fines for both parties were "unjustifiably harsh", the Thebans probably expected neither party to pay, and thus to be able to declare a "sacred war" on either.
Third Sacred War
In early 346 BC, Philip let it be known that he intended to march south with the Thessalians, though not where or why. The Phocians thus made plans to defend Thermopylae, and requested assistance from the Spartans and the Athenians, probably around 14 February. The Spartans dispatched Archidamus III with 1,000 hoplites, and the Athenians ordered everyone eligible for military service under the age of 40 to be sent to the Phocians' aid. However, between the Phocians' appeal and the end of the month, all plans were upset by the return of Phalaikos to power in Phocis; the Athenians and the Spartans were subsequently told that they would not be permitted to defend Thermopylae. It is not clear from the ancient sources why Phalaikos was returned to power, nor why he adopted this dramatic change of policy. Cawkwell suggests, based on remarks of Aeschines, that the Phocian army restored Phalaikos because they had not been properly paid, and further that Phalaikos, realizing that the army could not be paid and that the Phocians could no longer hope to win the war, decided to try to negotiate a peace settlement with Philip.