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
At some point during his campaigns in Thessaly, Philip captured the strategic port of Pagasae, which was in effect the port of Pherae. It is unclear whether this was during the first or second campaign; both Buckler and Cawkwell suggest that it took place in the second campaign, before the Battle of Crocus Field. By taking Pagasae, it is possible that Philip prevented Pherae from being reinforced by sea during his second campaign. Buckler suggests that Philip had learnt his lesson from the previous campaign, and intended to cut Pherae off from outside help before attacking it.