In 279 BC, the narrow pass of Thermopylae in Greece once again became the site of a pivotal battle. But instead of the famous last stand of Leonidas and his 300 Spartans against the Persians, this forgotten clash pitted an invading Celtic army against a loose coalition of Greek city-states. The Celtic attack on Delphi represented the high water mark of the great Celtic migrations that reshaped much of Europe in the early Hellenistic period. Though ultimately defeated, the Celts came within a hair‘s breadth of striking at the heart of the Greek world, and their brief triumph at Thermopylae highlighted the weaknesses of a divided Greece.
The Celtic Invasion of Greece
The Celts who threatened Greece in 279 BC were part of a vast network of related tribes that dominated much of Western and Central Europe. Originating in the upper Danube region, these Celts had migrated and raided far beyond their homelands in the preceding centuries. Celtic bands had sacked Rome in 390 BC, invaded Thrace and Macedon in 310 BC, and even crossed into Asia Minor to found the kingdom of Galatia.[^1]
The Greek historian Pausanias vividly described the terror these "barbarians" inspired:
The Celts are the tallest of men and the most warlike; and their courage is supported by numbers and boldness. They have a loud and terrifying voice, and delight in exaggerating their natural ferocity of expression by wearing horrid masks and imitating wild beasts.[^2]
In 279 BC, one of the largest Celtic forces yet seen invaded Greece, led by the warlord Brennus. Ancient sources give wildly inflated figures for the size of his army, from 152,000 infantry and 20,400 cavalry to 300,000 warriors in total.[^3] Modern historians estimate a more plausible but still formidable force of 30,000-50,000 men.[^4]
Brennus aimed to strike at the wealthy sanctuary of Delphi, the navel of the Greek world. To reach it, he first had to advance through the narrow pass at Thermopylae, known as the "Hot Gates" for its sulfur springs. On the other side, a rare alliance of rival Greek states prepared to stop him.
The Greek Coalition
News of the approaching Celtic horde spurred the normally fractious Greeks to unite in defense. The Aetolian League, controlling most of central Greece, provided the largest contingent of 7,000 hoplites and 700 cavalry. Athens sent its fleet and 1,000 infantry, while Boeotia mustered 10,000 foot and 500 horse. Phocis raised 3,000 men, and other allies like Megara added their strength.[^5]
This coalition force of over 20,000 men assembled at Thermopylae under the nominal leadership of the Athenian general Callippus. They chose to make their stand there, well aware of the legendary defensive potential of the pass. In 480 BC, a small force of Greeks led by 300 Spartans had held off a far larger Persian army for three days at Thermopylae before being outflanked and annihilated.[^6]
Could history repeat itself, or would the Greeks fare better against these new barbarian invaders? The answer would depend on the battle-field performance of the armies, which differed greatly in arms and tactics.
Celtic and Greek Warfare
The Celts were renowned for their ferocity in battle, fighting with a berserker fury that often shocked more disciplined foes. Celtic warriors typically eschewed armor in favor of mobility, wearing only trousers and cloaks, and sometimes fought entirely naked to display their bravery.[^7] Their primary weapons were long slashing swords, javelins, and wooden shields.
In contrast, Greek hoplites were heavily armed and armored, prioritizing protection and cohesion over individual prowess. They wore bronze helmets, breastplates, and greaves, and carried large round shields called hoplons. Their main weapon was a long thrusting spear, supplemented by a short sword.[^8]
The Greeks fought in close-ordered phalanx formation, presenting a wall of overlapping shields to the enemy. This tactic was well-suited for holding a narrow front like Thermopylae but less mobile and flexible than the looser Celtic style. The clash of these two warrior cultures would be decided by the specific conditions and leadership at Thermopylae.
The Battle Begins
As the Celts descended into Greece, they ravaged the countryside, despoiling tombs and sacking towns. Reaching Thermopylae, Brennus arrayed his host before the pass and demanded that the Greeks lay down their arms and depart. When they refused, he ordered a frontal assault along the narrow strip of land between the mountains and the sea.[^9]
The first day of battle showcased the strengths of both sides but gave the Greeks a tactical edge. The Athenian fleet deployed along the adjacent coastline, pouring volleys of arrows and javelins into the exposed flank of the massed Celtic warriors. The Greek phalanx held firm in the close quarters of the pass, a wall of shields and spear points that the Celts could not break through.
According to Pausanias, the Celts attacked with reckless abandon, fighting on despite gruesome wounds:
They rushed at their adversaries like wild beasts, full of rage and void of reason. Some of them pulled the spears they were hit by out of their wounds and threw or stabbed with them, heedless of their injuries.[^10]
Despite suffering horrific losses, the Celts drew on reinforcements to launch attack after attack, hoping to overwhelm the Greek line with sheer numbers. By nightfall, neither side had gained a decisive advantage, but Greek discipline and firepower had inflicted a heavy toll on the barbarian horde.
The Aetolian Diversion
Realizing he could not break through by brute force alone, Brennus sought another way. He learned that a large contingent of the Greek defenders hailed from Aetolia in central Greece. To draw them away from Thermopylae, he detached 40,000 men under two subordinates, Combutis and Orestorius, with orders to march west and ravage Aetolian lands.[^11]
The marauding Celts fell upon the border town of Callion, sacking it with savage cruelty. Pausanias recorded the slaughter:
They butchered every human male of that entire race, the old men and the children at the breast. Any woman and mature virgin with a spark of pride killed themselves as soon as the city fell. Those who lived were subjected with wanton violence to every form of outrage by men as remote from mercy as they were remote from love.[^12]
When word of this atrocity reached the 7,000 Aetolians guarding Thermopylae, they felt compelled to leave immediately to defend their homes – a quarter of the Greek force. The loss of these troops left a dangerous gap in the Greek line, one that Brennus intended to exploit.
Outflanked and Overwhelmed
While the Aetolians rushed to confront the marauders, Brennus executed the masterstroke of his battle plan. He bribed local Greek informants to guide 40,000 of his best troops along a mountain path that bypassed the pass, the same route the Persians had used to outflank the Spartans centuries before.[^13]
This path was guarded by 1,000 Phocians, but a thick fog concealed the Celtic approach until it was too late. The Phocians were overwhelmed, and only a few escaped to give warning. Plutarch described the grim scene:
The violence of the oncoming Celts was irresistible, and the Phocians, after losing many men, fled to spread the alarm. It was now late afternoon, and the Celts were on the point of descending into the plain beyond Thermopylae.[^14]
Brennus‘s main Celtic army attacked into the front of the pass, while his flanking force charged down on the Greek rear. Callippus, seeing the trap sprung, ordered an immediate retreat to the waiting Athenian ships. The Greek army dissolved into chaos, engaged in a furious rearguard fight through the defile as they raced for the shore.[^15]
Amidst this desperate struggle, the Athenian fleet stood close inshore to ferry the survivors aboard, enduring volleys of javelins from the oncoming Celts. Many Greeks fell or drowned in the surf, but the majority made it onto the ships and escaped. By sunset, the battle was over, and the Celts held the pass.
Aftermath and Legacy
The Greek survivors limped back to their home cities, while the Celts advanced virtually unopposed through the rest of central Greece. Arriving at the sanctuary of Delphi, Brennus gave his men free rein to pillage its legendary treasures but met unexpected resistance from a hastily assembled Greek force.
In the ensuing battle beneath the temple walls, Brennus was wounded, and his army suffered heavily. Demoralized and depleted, the Celts retreated from Delphi. According to Greek legend, a divine intervention of earthquakes, rockfalls, and phantom warriors had aided in their defeat.[^16]
The surviving Celts withdrew from Greece, though splinter groups settled in Thrace and Anatolia. The main Celtic invasion was over, but it had come perilously close to striking the sacred heart of the Greek world. This near-miss resulted from Greek disunity, as the Aetolian contingent prioritized their local defense over holding Thermopylae.
The Celtic triumph also highlighted the strengths and weaknesses of each army. In a frontal clash in close quarters, the armored phalanx could hold against Celtic ferocity. But when flexibility and maneuver were needed to react to a flanking threat, the phalanx was dangerously rigid.
More broadly, the brief rupture of Thermopylae underscored the dilemma facing the Greeks in a dangerous new world. The rise of Macedon under Alexander the Great had shattered the old political balance, and migrating "barbarians" like the Celts and later the Romans threatened the divided Greek city-states. As one modern historian put it:
The battle of Thermopylae in 279 BC was a minor event, which would have been forgotten if it had not been the prelude to the dramatic attack of Delphi. But it was symbolic. Once again, the Greeks had faced and defeated an external threat, but it showed that the door of Greece was no longer locked.[^17]
Thermopylae remains a potent symbol of courage against the odds, but its forgotten Celtic sequel is a reminder that the bravest sacrifices cannot always salvage a lost cause. If the story of Leonidas and his 300 Spartans has echoed through the ages, the grim fate of Callippus and his Athenians might stand as an unheeded warning for the new perils of a disunited Greece on the eve of its loss of independence.
[^1]: Rankin, D. (1996). Celts and the Classical World. Routledge. pp. 78-89.[^2]: Pausanias. Description of Greece, 10.19.4-5.
[^3]: Diodorus Siculus. Library of History, 22.9.
[^4]: Gilliver, K., Whitby, M., & Goldsworthy, A. (2005). Rome at War: Caesar and His Legacy. Osprey Publishing. p. 80.
[^5]: Scholten, J. B. (2000). The Politics of Plunder: The Aetolians and their Koinon in the Early Hellenistic Era. University of California Press. p. 143.
[^6]: Herodotus. The Histories, 7.201-239.
[^7]: Livy. The History of Rome, 38.21.
[^8]: Hanson, V. D. (2009). The Western Way of War: Infantry Battle in Classical Greece. University of California Press. pp. 55-84.
[^9]: Pausanias. Description of Greece, 10.19.11.
[^10]: Ibid., 10.21.2.
[^11]: Justin. Epitome of Pompeius Trogus, 24.5.
[^12]: Pausanias. Description of Greece, 10.22.2.
[^13]: Ibid., 10.22.8.
[^14]: Plutarch. Moralia, 244F.
[^15]: Polyaenus. Stratagems, 7.35.2.
[^16]: Pausanias. Description of Greece, 10.23.1-2.
[^17]: Green, P. (1996). The Greco-Persian Wars. University of California Press. p. 17.
