Expansion of Macedonia under Philip II
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 ostensibly 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
Meanwhile, Onomarchos returned to Thessaly to try to preserve the Phocian ascendancy there, with approximately the same force as during the previous year. Furthermore, the Athenians dispatched Chares to help their Phocian allies, seeing the opportunity to strike a decisive blow against Philip. Subsequent events are unclear, but a battle was fought between the Macedonians and the Phocians, probably as Philip tried to prevent the Phocians uniting forces with the Pheraeans, and crucially, before the Athenians had arrived. According to Diodorus, the two armies met on a large plain near the sea, probably in the vicinity of Pagasae. Philip sent his men into battle wearing crown of laurel, the symbol of the Apollo; "as if he was the avenger...of sacrilege, and he proceeded to battle under the leadership, as it were, of the god". In the ensuing battle, the bloodiest recorded in ancient Greek history, Philip won a decisive victory against the Phocians. In total, 6,000 Phocian troops were killed including Onomarchos, and another 3,000 taken prisoner. Onomarchos was either hanged or crucified and the other prisoners drowned, as ritual demanded for temple-robbers. These punishments were designed to deny the defeated an honourable burial; Philip thus continued to present himself as the pious avenger of the sacrilege committed by the Phocians.