The Celtic Battle of Thermopylae | History Hit

The Celtic Battle of Thermopylae

Thermopylae, as depicted in Edward Dodwell's 'Views in Greece', 1821.
Image Credit: Public Domain

A large Celtic army led by the warlord Brennus descended on Greece in 279 BC, intent on pillaging its riches. But standing in their way was a formidable coalition of Greek forces, united to face off against this ‘barbarian’ incursion. It would be at the famous Thermopylae – ‘The Hot Gates’ – that the two sides faced off. Some 200 years earlier, Leonidas’ Spartans and their allies had fought their own legendary battle at this site against the Persian Empire.

The other battle of Thermopylae

Having successfully crossed the River Sperchius, Brennus wasted no time in advancing his army to the Hot Gates. He arranged his army at the northern end of the Pass. Battle was imminent. Leading his forces up the path in response was Callippus and the Greek army prepared to face the Celtic horde. Brennus’ warriors, eager for battle and encouraged by promises of unimaginable wealth that awaited them with victory, were all too happy to oblige. The forces collided. 

Leonidas Monument at Thermopylae

Image Credit: Public Domain

Death in the pass

The fighting was fierce on either side. For a whole day the pass would be filled with the sounds of battle, each side desiring victory at all costs. The power of the Celtic warrior was formidable, each individual a deadly fighter. Yet brawn and ferocity was not the answer to everything in ancient warfare.

In the narrow passage of Thermopylae, Greek discipline and cohesion quickly proved its worth. The solid Greek phalanx was in its element, as it was designed specifically with defence in mind. With the phalanx holding, the Greek Antigonus’ navy now also revealed its deadliness. Sailing next to the coastline, these ships rained a hail of arrows and various other missiles into the vulnerable flank of the Celtic army, dealing catastrophic damage and panic into the clustered enemy lines. The innumerable size of the Celtic horde, combined with their lack of armour, meant almost every arrow found a mark.

Celtic fury

Yet defiantly, the Celts pressed on, driven by a mad frenzy. Pausanias recalled how “They rushed at their adversaries like wild beasts, full of rage and temperament, with no kind of reasoning at all; they were chopped down with axes and swords but the blind fury never left them while there was breath in their bodies; even with arrows and javelins sticking through them they were carried on by sheer spirit while their life lasted.”

“Some of them even pulled the spears they were hit by out of their wounds and threw them or stabbed with them,” he added.

By the end of the day, neither side had made a breakthrough. As the sun set, both sides retreated, the Greeks to the southern end of the pass and the Celts to their camp on the Sperchius plain. Callippus and the Greeks claimed victory, but the battle was far from over.

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Down but not out

Brennus’ army had suffered heavily in the attack. The discipline of the Greek phalanx combined with the deadly barrage from the Athenian navy and the light infantry had ensured Thermopylae had become a killing ground for the attacking horde. Yet the sheer size of the army – allegedly over 150,000 strong – meant the Celtic force still vastly outnumbered their Greek foe.

Despite the significant numerical advantage, Brennus had no intention of attempting another frontal assault. He therefore ordered his army to explore the nearby region, hoping to find a way around the pass. But as the Celts scouted the area, they encountered the Greek force at the temple of Athena. Keen for plunder and booty, the horde descended on the temple. The small Greek garrison put up an almighty fight and repelled the assault. The Celts were driven off Mount Oeta, back to the plain.

After another setback, the Celts started to lose heart. They had been repulsed in all their efforts; another devastating frontal assault on the Pass looked inevitable. Instead, Brennus devised a brutal yet effective plan.

Divide and conquer

Thanks to information he had acquired, most likely from Greek deserters, Brennus knew the size and strength of Callippus’ force occupying Thermopylae. Among the Greek force was a large contingent of soldiers from the Aetolian League, the most powerful state in Greece at that time. Nearly 8,000 Aetolian volunteers had arrived at the pass to aid the defence – almost a third of the entire Greek force! Their presence was no doubt critical to the defence. Brennus therefore devised a solution to rid himself of these opposing soldiers.

Selecting just over 40,000 men for the task, Brennus ordered these warriors to march back across the Sperchius river and head west, towards Aetolia. Their mission was simple and ruthless: they were to inflict as much death and destruction on an Aetolian town as possible and let the fear spread. The rumours of the havoc the Celts had created in Paeonia, Macedonia and Thessaly was about to become a stark reality for the Aetolians.

Under the command of two of Brennus’ commanders, Cambutis and Orestorius, these warriors set off. They carried it out with deadly efficiency at a town that would forever become associated with some of the most atrocious war crimes in antiquity.

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Situated on the border of the region, Callion was the gateway to Aetolia from Thessaly. For the Celts, its location was thus ideal for their mission. It was the perfect place to send a message to the Aetolian force at Thermopylae; the perfect place from where they could threaten to unleash their full fury on the Aetolian heartlands.

What happened next was unbelievable slaughter. Pausanias recalls:

They butchered every human male of that entire race, the old men and the children at the breast… Any woman and mature virgins 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.

Pausanias, 10. 22. 2

Callion had been destroyed – its inhabitants slaughtered, houses plundered and sanctuaries set alight. 

Word spreads

News of the Callion atrocity soon reached Callippus’ army at Thermopylae – and the Aetolians. Aghast, these men feared the Celts would descend into their homeland; their cities, families and belongings now appeared under threat from suffering a similar fate to Callion. They could hardly stand idly by and let this happen.

Very quickly, the Aetolians at Thermopylae reached a decision. Desiring to defend their homeland, the 8,000 men abandoned the Thermopylae defence and headed home in all haste. They likely feared it was already too late. Yet unknown to them, these Celts had no intention of marching further into Aetolia. Having sacked Callion, they headed back towards Brennus’ main army and Thermopylae. Their mission was complete.

Brennus’ ruthless plan succeeded spectacularly. With the departure of the Aetolians, Brennus now had a window where the Greek defence was considerably weakened. 

The Mountain Pass

As Cambutis and Orestorius’ force laid waste to Callion, Brennus had been sending more scouting parties into the region between the Sperchius and the Pass – this time avoiding what remained of the garrison at the temple of Athena. Their aim had been simple: to find another route that would bypass the Hot Gates. Brennus soon received reports from his scouts that they had discovered the famed mountain path of antiquity. If he could march his army along these passes, then Brennus knew he could bypass and surround the Greek defence entrenched at Thermopylae; the road to Delphi would lie open. This was his opportunity.

Yet Callippus had prepared for this possibility. The Phocian garrison he had placed defending the path remained strong, ready to give everything to protect their comrades. Would they be able to hold against the impending Celtic attack? Gathering a sizable portion of his army, Brennus led these men towards the entrance of the mountain path near Heraclea. The rest of the army remained at Thermopylae, under the command of Brennus’ deputy, Achichorius, awaiting the given signal to strike. Everything depended on the success of Brennus’ manoeuvre.

The mist

At night, 40,000 Celts advanced down the path in the footsteps of Hydarnes. Fearing for their lives if they did not oblige, Brennus had enlisted the help of local guides to aid him along the path. With their guidance, he and his Celtic force quickly made great progress, arriving at the Phocian defence in the early morning. More good fortune was to follow. As Brennus and his army approached, a great mist descended, obscuring their advance from the Phocian defenders. Seizing the initiative, Brennus wasted no time in ordering the attack, hoping to take his foe by complete surprise.

The result was devastating. Caught completely off-guard, defeat soon followed for the defending Phocians. Thanks to the mist, they never stood a chance.

The final attack of Brennus at Thermopylae.

Fighting bravely despite the hopelessness of the situation, some managed to retreat to the pass, informing Callippus and their Greek comrades of their fate; many others however, would never leave the narrow defile, cut down by Brennus’ ferocious warriors. Brennus now had complete control of the pass. He ordered the advance; victory was near.

Reaching the end of the track and emerging behind the Greek defence, Brennus now ordered the main attack. Carnyx horns echoed through the pass, informing Achichorius and the main Celtic army that this was the moment they had been waiting for. The final assault had begun.


Unlike their Spartan predecessors, the Greeks were not resigned to suffer a similar fate of a heroic-but pointless last stand. They intended to survive!

Learning from the retreating Phocians that their defence had collapsed, Callippus had hastily ordered a desperate retreat. Thousands of Greek soldiers descended to the shoreline, scrambling to board Antigonus’ Athenian ships that were ready to evacuate them. But time was not on their side; both Brennus and Achichorius’ bloodthirsty warbands were closing in.

With their backs to the sea, a desperate struggle erupted between the Greek rearguard and the Celts, fighting all the way to the ships. Yet in the end, Callippus’ order to withdraw had come just in time. Thanks to heroic fighting from the Greek rear-guard, most of the army was evacuated. Truly this was the Dunkirk-equivalent of antiquity.

Yet although Callippus and his Greeks could perhaps take some comfort from this success, the reality was far bleaker. They had failed to defeat Brennus and his Celtic horde at the place best-suited to prevent the invasion. Nothing now prevented these barbarians from marching on the epicentre of Hellenic culture: Delphi. They needed a miracle.

Tristan Hughes