Battle of Leuctra
The first recorded use of a tactic similar to the oblique order was in 371 BC at the Battle of Leuctra, when the Thebans under Epaminondas defeated the Spartans by reinforcing one flank to fifty rows deep, rather than spreading their troops evenly across the front. Philip of Macedon learned Epaminondas' technique while held prisoner at Thebes, and his successors, including Alexander the Great, used it in their campaigns.