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.
Theban–Spartan War
The Sacred Band first saw action in 378 BC, at the beginning of the Boeotian War. It was during the famous stand-off between the Athenian mercenary commander (and later "strategos") Chabrias (d. 357 BC) and the Spartan King Agesilaus II (444 BC–360 BC). Prior to the creation of the Sacred Band under Gorgidas, the Athenians had helped the Theban exiles retake control of Thebes and the citadel of Cadmea from Sparta. This was followed by Athens openly entering into an alliance with Thebes against Sparta. In the summer of 378 BC, Agesilaus led a Spartan expedition against Thebes from the Boeotian city of Thespiae (then still allied to Sparta). His force consisted of 1,500 cavalry and 28,000 infantry. At least 20,000 of the infantry were hoplites, while 500 were of the elite band of Sciritae (Σκιρῖται) light infantry vanguard. Learning of the impending invasion, Athens quickly came to the aid of Thebes by sending a force of about 200 cavalry and 5,000 men (both citizen and mercenary, including hoplites and peltasts) under the command of the Athenian "strategos" Demeas and mercenary commander Chabrias.