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
His position now secure, Onomarchos had his chief opponents arrested and executed, and confiscated their property to add to his war-chest. He then set about raising a new army, doubling the size of Philomelos's force, until he had 20,000 men and 500 cavalry at his disposal. Raising such a large force required extensive depredations of Apollo's wealth; bronze and iron dedications were melted down and recast as weapons, whilst gold and silver offerings were melted down and used to make coinage. Although raising such a large army would have taken a considerable time, Onomarchos had the whole winter after Neon in which to do so.