The Battle of Crocus Field was a battle in the Third Sacred War, fought between the armies of Phocis, under Onomarchos, and the combined Thessalian and Macedonian army under Philip II of Macedon. In the bloodiest battle recorded in Ancient Greek history, the Phocians were decisively defeated by Philip's forces. Philip's victory secured his appointment as ruler of Thessaly, marking an important step in the rise of Macedon to political ascendancy in Ancient Greece.