Gallic groups from the La Tène chiefdoms began moving southeast into the Balkans around the 4th century BC. Gallic settlements were mostly located in the western part of the Carpathian basin, but some groups also moved into the Balkans.
From bases in northern Illyria and Pannonia, the Gallic invasions reached their peak in the early 3rd century BC, including an invasion of Greece. The invasion of Greece in 279 BC happened after earlier military actions in the southern Balkans and against the Kingdom of Macedonia. These actions were made easier by the confusion caused by disagreements over who would rule after Alexander the Great’s death. Some of the invading Celts crossed into Anatolia and eventually settled in the region that later became known as Galatia.
Settlement of southeastern Europe
Starting in the 4th century BC, Celtic groups moved into the Carpathian region and the Danube basin, at the same time as they moved into Italy. The Boii and Volcae were two large Celtic groups that often worked together during their military actions. Smaller groups traveled south through two main paths: one followed the Danube River, and the other went east from Italy. According to a legend, about 300,000 Celts moved into Italy and Illyria.
By the 3rd century BC, most of the original people living in Pannonia had adopted Celtic ways. Evidence of La Tène culture is found throughout Pannonia, but there are few such items beyond the Tisza and Sava rivers. These items are believed to be a local version of Celtic culture called Norican-Pannonian. However, some findings suggest the Celts had contact with distant areas like Iberia. The rich land near the rivers in Pannonia allowed the Celts to settle easily, grow crops, make pottery, and use the valuable mines in modern-day Poland. This shows that the Celts had created a new home for themselves in southern Central Europe, covering an area from Poland to the Danube River.
Early expeditions
The political situation in the northern Balkans changed often, with different tribes taking control over their neighbors at different times. Inside each tribe, a group of warriors who were skilled at moving quickly and taking advantage of opportunities led military actions. These warriors sometimes conquered large areas and controlled the people living there. During the 4th century BC, the political situation in the Balkans helped the Celts. The Illyrians were fighting the Greeks, which made their western side weaker. While Alexander the Great ruled Greece, the Celts did not dare to move south near Greece. Because of this, early Celtic attacks focused on Illyrian tribes.
The first Balkan tribe defeated by the Celts was the Illyric Autariatae. During the 4th century BC, this tribe had control over much of the central Balkans, with its main area near the Morava valley. Evidence of how the Celts fought can be seen in their attacks on the Ardiaei.
In 335 BC, the Celts sent envoys to Alexander the Great to show respect, while Macedon was fighting wars with the Thracians on its northern border. Some historians believe this act was actually a way to learn about Macedonian military strength. After Alexander the Great died, Celtic armies began moving toward southern areas, threatening the kingdom of Macedonia and the rest of Greece. In 310 BC, the Celtic general Molistomos attacked deep into Illyrian lands, trying to control the Dardanians, Paeonians, and Triballi. However, Molistomos was defeated by the Dardanians. The new Macedonian king, Cassander, decided to protect some of his former enemies from the Illyrians, even though the Illyrians had won the battle. In 298 BC, the Celts tried to attack Thrace and Macedon but were heavily defeated near Haemus Mons by Cassander. However, another group of Celts, led by the general Cambaules, marched into Thrace and captured large areas. The Celtic tribe known as the Serdi lived in Thrace and built the city of Serdica, which is now called Sofia.
Invasions of Thrace and Greece
In 281 BC, the Celtic military actions in southern Greece and the Balkans reached an important moment. The fall of Lysimachus' kingdom in Thrace allowed the Celts to move into the region. Different sources explain the reason for their migration: Pausanias said it was because of a desire for treasure, Justin believed it was due to overpopulation, and Memnon thought it was caused by a lack of food. Pausanias also wrote that a small group led by Cambaules first tried to attack but left when they realized they were too few. In 280 BC, a large army of about 85,000 warriors left Pannonia and split into three groups. They marched south toward Macedon and central Greece. One group, led by Cerethrius, attacked the Thracians and Triballi. Another, led by Brennus and Acichorius, targeted the Paionians. The third group, under Bolgios, aimed at the Macedonians and Illyrians.
Bolgios caused heavy losses to the Macedonians, capturing and killing their young king, Ptolemy Keraunos. However, Bolgios' forces were later driven back by a Macedonian noble named Sosthenes. Sosthenes was then defeated by Brennus and his group, allowing them to attack the region.
After returning home, Brennus encouraged a third large attack on central Greece, led by himself and Acichorius. The reported army size of 152,000 foot soldiers and 24,400 horsemen was likely exaggerated. Pausanias explained that the cavalry used a tactic called trimarcisia, where each rider had two helpers on horses to support them during battles.
A Greek alliance, including the Aetolians, Boeotians, Athenians, Phocians, and others north of Corinth, set up a defensive position at the narrow pass of Thermopylae. Brennus' forces suffered heavy losses during the first attack and sent Acichorius to attack Aetolia. The Aetolians left Thermopylae to defend their homes, but they fought fiercely using hit-and-run tactics. Only about half of Acichorius' group returned from Aetolia.
Brennus eventually found a way around Thermopylae, but the Greeks had already escaped by sea. He then marched to Delphi, where he was defeated and forced to retreat. Brennus later died from wounds sustained in the battle. His army was later defeated by the Thessalians and Malians near the Spercheios River.
Historians Pausanias and Justinus both wrote that the Gauls were defeated at Delphi. A violent storm made it hard for the Gauls to move or hear orders. After a frosty night, the Greeks attacked from both sides, and Brennus was wounded. The Gauls fell back, killing their injured soldiers who could not retreat. That night, panic spread in the camp, and the Gauls fought among themselves. They were eventually driven back by the Greeks. Brennus either drank wine to end his life, as Pausanias said, or stabbed himself, according to Justinus.
The Romans later told a different story about the events at Delphi. Strabo wrote about a legendary treasure called aurum Tolosanum, which was said to be 15,000 talents of gold and silver stolen during the attack on Delphi. The treasure was supposedly brought to Tolosa (modern Toulouse, France) by the Tectosages, part of the invading army.
Over 150 years later, in 105 BC, the Roman general Quintus Servilius Caepio looted Tolosa, finding 50,000 gold bars and 10,000 silver bars. The silver was sent to Rome, but the gold was stolen by marauders believed to be hired by Caepio. The gold was never found and was said to have passed to Marcus Junius Brutus, a descendant of Caepio's family.
In 105 BC, Caepio refused to work with his superior officer, Gnaeus Mallius Maximus, and chose to fight the Cimbri on the Rhone River. His army was destroyed in the Battle of Arausio. Caepio was later tried in Rome for losing his army and misusing funds. He was stripped of his citizenship, fined heavily, and exiled. His defeat was seen as punishment for stealing sacred treasure.
Strabo doubted the story of the treasure, arguing that the Gauls could not have carried such riches and that Delphi had already been robbed by the Phocians earlier. However, some modern historians still believe the attack on Delphi was real.
After the Greek campaigns
Most scholars consider the Greek campaign a failure for the Celts.
Some Celts who survived the Greek campaign, led by Comontoris (a general under Brennus), settled in Thrace. In 277 BC, Antigonus II Gonatas defeated the Gauls at the Battle of Lysimachia, forcing the survivors to retreat and establish a short-lived city-state called Tyle. Another group of Gauls, who separated from Brennus’ army in 281 BC, were sent to Asia Minor by Nicomedes I to help him defeat his brother and claim the throne of Bithynia. These Gauls eventually settled in a region later named Galatia. They were later defeated by Antiochus I, which led to their confinement in barren highlands in central Anatolia.
From the 4th to the 1st century BC, Celtic groups remained the most powerful political units in the northern Balkans. The Boii controlled much of northern Pannonia during the 2nd century BC and are also mentioned as having occupied the area now known as Slovakia. Other tribes of the Boian confederation lived in Pannonia, including the Taurisci in the upper Sava valley, west of Sisak, and the Anarti, Osi, and Cotini in the Carpathian basin. In the lower Sava valley, the Scordisci held strong influence over their neighbors for more than a century.
In the later half of the 1st century BC, power dynamics among barbarian tribes in Pannonia changed significantly. The defeat of the Boian confederation by the Geto-Dacian king Burebista reduced Celtic control of the Carpathian basin and reversed some Celtic influence. However, new Celtic tribes appear in historical records. The Hercuniates and Latobici moved from northern regions (Germania), and new tribes with Latin names, such as the Arabiates, emerged, possibly formed from remnants of the defeated Boian confederation. To weaken Celtic dominance, the Romans relocated the Pannonian-Illyrian Azali to northern Pannonia. Over time, Celtic political power in the region was replaced by newer barbarian groups, such as the Marcomanni and Iazyges. The Celts gradually lost their ethnic independence as they were absorbed by neighboring Dacian, Illyrian, and Germanic peoples. However, Celtic names continued to appear in records until the 3rd century AD.