Battle of Leuctra (371 B.C.)
A battle fought on the plain of Leuctra in southern Boeotia, in which a Boeotian army under Epaminondas defeated a Spartan army under King Cleombrotus. This Spartan defeat in the Boeotian-Athenian war against Sparta of 379-371 destroyed the reputation of the Spartan hoplite phalanx and established Theban hegemony in Greece (371-362). Epaminondas' tactical innovations of oblique order and concentration of forces against the enemy's command brought about the Theban-Boeotian victory.
After the Theban refusal to sign the peace agreement of 371, Cleombrotus, who was in Phocis with about 10,000 Spartan and allied hoplites and 1,000 cavalry, was ordered to invade Boeotia and attack Thebes. He was met by Epaminondas' Theban force, consisting of about 6,000 hoplites (heavily armed infantrymen) and an unknown number of cavalry. Eschewing the usual battle formation of cavalry heading a continuous hoplite phalanx, with the commander on the right wing, Epaminondas massed hoplites to a depth of 50 on his left wing and advanced it ahead of the centre and right wings. When the superior Theban cavalry drove the Spartan cavalry back on the phalanx, the Theban left wing attacked and routed the Spartan right, killing Cleombrotus, the Spartan king. Xenophon, a contemporary historian, reports nearly 1,000 Spartan dead. (Encyclopaedia Britannica Online.)