Gallic invasion of the Balkans Gallic groups , originating from the various La Tène chiefdoms , began a southeastern movement into the Balkan peninsula from the 4th century BC . Although Celtic settlements were concentrated in the western half of the Carpathian basin , there were notable incursions , and settlements , within the Balkan peninsula itself . From their new bases in northern Illyria and Pannonia , the Gallic invasions climaxed in the early 3rd century BC , with the invasion of Greece . The 279 BC invasion of Greece proper was preceded by a series of other military campaigns waged toward the southern Balkans and against the kingdom of Macedonia , favoured by the state of confusion ensuing from the intricated succession to Alexander . A part of the invasion crossed over to Anatolia and eventually settled in the area that came to be named after them , Galatia . Settlement of Southeastern Europe . From the 4th century BC , Celtic groups pushed into the Carpathian region and the Danube basin , coinciding with their movement into Italy . The " Boii " and " Volcae " were two large Celtic confederacies who generally cooperated in their campaigns . Splinter groups moved south via two major routes : one following the Danube river , another eastward from Italy . According to legend , 300 , 000 Celts moved into Italy and Illyria . By the 3rd century , the native inhabitants of Pannonia were almost completely Celticized . La Tene remains are found widely in Pannonia , but finds westward beyond the Tisza river and south beyond the Sava are rather sparse . These finds are deemed to have been locally produced " Norican - Pannonian " variation of Celtic culture . Nevertheless , features are encountered which suggest ongoing contacts with distant provinces such as Iberia . The fertile lands around the Pannonian rivers enabled the Celts to establish themselves easily , developing their agriculture and pottery , and at the same time exploiting the rich mines of modern Slovenia . Thus it appears that the Celts had created a new homeland for themselves in Southeastern Europe - centred in a region stretching from Vienna to the river Tisa . Early expeditions . The political situation in the northern Balkans was in constant flux with various tribes dominant over their neighbors at any one time . Within tribes , military expeditions were conducted by " an enterprising and mobile warrior class able from time to time to conquer large areas and to exploit their population " . The political situation in the Balkans during 4th century BC played to the Celts ' advantage . The Illyrians had been waging war against the Greeks , leaving their western flank weak . While Alexander ruled Greece , the Celts dared not to push south near Greece . Therefore , early Celtic expeditions were concentrated against Illyrian tribes . The first Balkan tribe to be defeated by the Celts was the Illyric Autariatae , who , during the 4th century BC , had enjoyed a hegemony over much of the central Balkans , centred on the Morava valley . An account of Celtic tactics is revealed in their attacks on the Ardiaei . In 335 BC , the Celts sent representatives to pay homage to Alexander the Great , while Macedon was engaged in wars against Thracians on its northern border . Some historians suggest that this ' diplomatic ' act was actually an evaluation of Macedonian military might . After the death of Alexander the Great , Celtic armies began to bear down on the southern regions , threatening the Greek kingdom of Macedonia and the rest of Greece . In 310 BC , Celtic general Molistomos attacked deep into Illyrian territory , subduing the Dardanians , Paeonians and Triballi . The new Macedonian king Cassander felt compelled to take his old Illyrian enemies under his protection . In 298 BC , the Celts attempted a penetrating attack into Thrace and Macedon where they suffered a heavy defeat near Haemus Mons at the hands of Cassander . However , another body of Celts led by the general Cambaules marched on Thrace , capturing large areas . Invasions of Greece . " Great expedition " of 279 BC . The Celtic military pressure toward Greece in the southern Balkans reached its turning point in 281 BC . The collapse of Lysimachus ' successor kingdom in Thrace opened the way for the migration . The cause for this is explained by Pausanias as greed for loot , by Justin as a result of overpopulation , and by Memnon as the result of famine . According to Pausanias , an initial probing raid led by Cambaules withdrew when they realized they were too few in numbers . In 280 BC a great army , comprising about 85 , 000 warriors , coming from Pannonia and split into three divisions , marched South in a " great expedition " to Macedon and central Greece . Under the leadership of Cerethrius , 20 , 000 men moved against the Thracians and Triballi . Another division , led by Brennus and Acichorius moved against Paionia ns while a third division , headed by Bolgios , aimed for Macedonians and Illyrians . Bolgios inflicted heavy losses on the Macedonians , whose young king , Ptolemy Keraunos , was captured and decapitated . However , Bolgios ' contingent was repulsed by the Macedonian nobleman Sosthenes , and satisfied with the loot they had won , Bolgios ' contingents turned back . Sosthenes , in turn , was attacked and defeated by Brennus and his division , who were then free to ravage the country . After these expeditions returned home , Brennus urged and persuaded them to mount a third united expedition against central Greece , led by himself and Acichorius . The reported strength of the army of 152 , 000 infantry and 24 , 400 cavalry is impossibly large . The actual number of horsemen has to be intended half as big : Pausanias describes how they used a tactic called " trimarcisia " , where each cavalryman was supported by two mounted servants , who could supply him with a spare horse should he have to be dismounted , or take his place in the battle , should he be killed or wounded . Battle of Thermopylae ( 279 BC ) . A Greek coalition made up of Aetolians , Boeotians , Athenians , Phocians , and other Greeks north of Corinth took up quarters at the narrow pass of Thermopylae , on the east coast of central Greece . During the initial assault , Brennus ' forces suffered heavy losses . Hence he decided to send a large force under Acichorius against Aetolia . The Aetolian detachment , as Brennus hoped , left Thermopylae to defend their homes . The Aetolians joined the defense en masse - the old and women joining the fight . Realizing that the Gallic sword was dangerous only at close quarters , the Aetolians resorted to skirmishing tactics . According to Pausanias , only half the number that had set out for Aetolia returned . Eventually Brennus found a way around the pass at Thermopylae but the Greeks escaped by sea . Attack on Delphi . Brennus pushed on to Delphi where he was defeated and forced to retreat , after which he died of wounds sustained in the battle . His army fell back to the river Spercheios where it was routed by the Thessalians and Malians . Both historians who relate the attack on Delphi , Pausanias and Junianus Justinus , say the Gauls were defeated and driven off . They were overtaken by a violent thunderstorm which made it impossible to manoeuvre or even hear their orders . The night that followed was frosty , and in the morning the Greeks attacked them from both sides . Brennus was wounded and the Gauls fell back , killing their own wounded who were unable to retreat . That night a panic fell on the camp , as the Gauls divided into factions and fought amongst themselves . They were joined by Acichorius and the rest of the army , but the Greeks forced them into a full - scale retreat . Brennus took his own life , by drinking neat wine according to Pausanias , by stabbing himself according to Justinus . Pressed by the Aetolians , the Gauls fell back to the Spercheios , where the waiting Thessalians and Malians destroyed them . Cursed Gold of Delphi . In spite of the Greek accounts about the defeat of the Gauls , the Roman literary tradition liked best a far different version . Strabo reports a story told in his time of a semi - legendary treasure - the " aurum Tolosanum " , fifteen thousand talents of gold and silver - supposed to have been the cursed gold looted during the sack of Delphi and brought back to Tolosa ( modern Toulouse , France ) by the Tectosages , who were said to have been part of the invading army . More than a century and a half past the alleged sack , Romans will rule the Gallia Narbonensis . In 105 BC , while marching to Arausio , the Proconsul of Cisalpine Gaul Quintus Servilius Caepio plundered the sanctuaries of the town of Tolosa , whose inhabitants had joined the Cimbri , finding over 50 , 000 15 lb . bars of gold and 10 , 000 15 lb . bars of silver . The riches of Tolosa were shipped back to Rome , but only the silver made it : the gold was stolen by a band of marauders , who were believed to have been hired by Caepio himself and to have killed the legion guarding it . The Gold of Tolosa was never found , and was said to have been passed all the way down to the last heir of the Servilii Caepiones , Marcus Junius Brutus . In 105 BC , Caepio refused to co - operate with his superior officer , Gnaeus Mallius Maximus , because he thought of him as a " novus homo " , deciding by himself to engage in battle against the Cimbri , on the Rhone . There the Roman army suffered a crushing defeat and complete destruction , in the so - called Battle of Arausio ( modern Orange ) . Upon his return to Rome , Caepio was tried for " the loss of his Army " and embezzlement . He was convicted and given the harshest sentence allowable ; he was stripped of his Roman citizenship , forbidden fire and water within eight hundred miles of Rome , fined 15 , 000 talents ( about 825 , 000 lb ) of gold , and forbidden from seeing or speaking to his friends or family until he had left for exile . He spent the rest of his life exiled in Smyrna in Asia Minor . His defeat and the ensuing ruin were looked upon as a punishment for his sacrilege theft . Strabo distances himself from this account , arguing that the defeated Gauls were in no position to carry off such spoils , and that , in any case , Delphi had already been despoiled of its treasure by the Phocians during the Third Sacred War in the previous century . However , Brennus ' legendary pillage of Delphi is presented as fact by some popular modern historians . After the Greek campaigns . Most scholars have deemed the Greek campaign a disaster for the Celts . However , others claim that permanent occupation was not their aim , rather they were intent on plundering the riches of the Greeks - which they did . Moreover , although they were expelled from Greece , their power in southeastern Europe was not at an end . Some of the survivors of the Greek campaign , led by Comontoris ( one of Brennus ' generals ) settled in Thrace . In 277 BC Antigonus II Gonatas defeated the Gauls at the Battle of Lysimachia and the survivors retreated founding a short - lived city - state named Tyle . Another group of Gauls , who split off from Brennus ' army in 281 , were transported over to Asia Minor by Nicomedes I to help him defeat his brother and secure the throne of Bithynia . They eventually settled in the region that came to be named after them as Galatia . They were defeated by Antiochus I , and as a result , they were confined to barren highlands in the center of Anatolia . Celtic groups were still the preeminent political units in the northern Balkans from the fourth to the 1st century BC . The " Boii " controlled most of northern Pannonia during the 2nd century BC , and are also mentioned to have occupied the territory of modern Slovakia . We learn of other tribes inhabiting Pannonia , belonging to the Boian confederation . There were the " Taurisci " in the upper Sava valley , west of Sisak , as well as the " Anarti " , " Osi " and " Cotini " in the Carpathian basin . In the lower Sava valley , the " Scordisci " wielded much power over their neighbours for over a century . The later half of the 1st century BC brought much change to the power relations of barbarian tribes in Pannonia . The defeat of the Boian confederation by the Geto - Dacian king Burebista significantly curtailed Celtic control of the Carpathian basin , and some of the Celticization was reversed . Yet , more Celtic tribes appear in sources . The Hercuniates and Latobici migrated from the northern regions ( Germania ) . Altogether new tribes are encountered , bearing Latin names ( such as the Arabiates ) , possibly representing new creations carved out of the defeated Boian confederation . To further weaken Celtic hegemony in Pannonia , the Romans moved the Pannonian - Illyrian " Azali " to northern Pannonia . The political dominance previously enjoyed by the Celts was overshadowed by newer barbarian confederations , such the Marcomanni and Iazyges . Their ethnic independence was gradually lost as they were absorbed by the surrounding Dacian , Illyrian and Germanic peoples , although Celtic names survive until the 3rd century AD .