6 July 371 BCE

A nineteenth-century print of the plan of the Battle of Leuctra in July 371 BCE shows clearly the novel tactic of the Theban leader, Epaminondas, in strengthening his left wing at the expense of his right in order to challenge the flat Spartan line.

When King Cleombrotus of Sparta marched along the Peloponnesian coast towards the town of Leuctra at the head of 10,000 Spartan and allied hoplites, the heavily armed infantry of Greek warfare, he must have been confident of victory. Sparta, with its rigorous military training and ethos of tough combat, had dominated the Greek world for a generation. Prudent city-states threw in their lot with Sparta and provided a good proportion of the men marching behind the Spartan king.

To defeat a Spartan host of this size would require either special courage or a novel battle plan. The commander who opposed Cleombrotus was the Theban soldier Epaminondas, and he possessed both. On a plain outside Leuctra, Sparta’s fearsome reputation was about to be blunted by a startling battlefield innovation.

The Spartans were marching to punish the city of Thebes for its efforts to dominate a cluster of cities in Boeotia, in central Greece. The Thebans were adept horsemen, in territory not well adapted to horse warfare. Together with some 6,500 hoplites raised from Thebes and their reluctant Boeotian allies, Epaminondas had 1,500 cavalry and 1,000 lightly armed peltasts, or skirmishers. The Theban hoplites had at their core the famous ‘Sacred Band’ of 300 selected men, who trained and fought in pairs and were also lovers, so it was said, in order to cement the soldierly bond between them.

They were led by Pelopidas, the key commander on the Theban side. Cleombrotus had with him 1,000 cavalry and 1,000 peltasts (the figures may be conjecture, but they give a sense of scale), but he relied on his powerful hoplite phalanx with its 400 royal guard, armed with breastplate, helmet and the deadly hoplite spear, the hoplon. When his force arrived on the plain near Leuctra he drew them up in conventional linear form, with a strong right wing containing the king and his guard, his weaker allies on the left and a force of cavalry and skirmishers in front. His phalanxes were twelve rows deep.

Epaminondas was already in position on higher ground. The Theban commander drew up his army in defiance of convention. On his left wing he created a narrow phalanx fifty rows deep, with an extraordinary weight of attack. At the centre and right he placed much shallower units, each one staggered back from the one in front in echelon formation. The cavalry was probably to the front, together with the peltasts. This was a risky strategy. If the Spartans could hold back the massive Theban phalanx, their left wing could sweep through the Theban right and encircle the enemy. Epaminondas perhaps gambled that the shock of his novel tactic would disorient the more numerous Spartans before they could adapt to the new battlefield situation. He also wanted to bring his best troops to battle first, leaving his unreliable Boeotian allies in the weaker echelons to the right. Whether that was the true motive for his novel formation, rather than a stroke of military genius, as some historians have argued, remains speculation.

The ancient sources, on which the account of the subsequent battle is based, differ considerably in detail. Only Xenophon, who was in Sparta at the time and is almost certainly the most reliable guide, described the use that Epaminondas made of the Theban cavalry. The battle opened, according to Xenophon, with a cavalry engagement that in some ways proved as decisive as the hoplite struggle that followed. The clash of horsemen produced an immediate panic among the Spartan cavalry, who rode back in confusion into their own hoplite ranks, breaking up the tight and disciplined formation typical of Spartan warfare.

Before the Spartans had a chance to regroup, the powerful Theban phalanx was pushing forward, with the Sacred Band at the front. Bloody hand-to-hand combat convulsed the Spartan right wing, while the left wing, uncertain of how to respond and composed of less reliable allies, found it difficult to engage with the weaker Theban front because of its staggered formation. By the time the left wing moved forward, the right wing was collapsing, exposing the whole Spartan force to encirclement.

The Theban strategy was fully justified by the results. Cleombrotus and most of his royal guard were slaughtered and the Spartans retreated, leaving at least 1,000 dead on the field (4,000 according to a later account). The remaining Spartan commanders requested a truce so that the dead and wounded could be carried away. The Thebans, rather than pursue the beaten enemy and risk a confrontation with Spartan reinforcements in the Peloponnese peninsula, withheld the coup de grâce, but the reputation of Sparta for invincibility was destroyed and the Thebans went on to wage victorious but more destructive battles at Cynoscephelae in 364 BCE, in which Pelopidas was hacked to death, and Mantinea two years later, where Epaminondas died from a spear thrust. His strategy survived him.

A young Macedonian, Philip, was almost certainly present at the time of Leuctra and was impressed by the Theban ploy. When he became King of Macedonia, Philip used the tactic to devastating effect, while his son Alexander the Great defeated the Persian Empire with a polished version of the oblique attack. Millennia later, Frederick II, King of Prussia, understood the significance of a battlefield innovation that was capable of evaporating Sparta’s aura of invincibility, and used it to his own advantage at the Battle of Leuthen in 1757.