The third century B.C. can be viewed as the last great period of Celtic expansion, with consequences that were felt throughout a vast area stretching from the British Isles and central Anatolia to the plains of northern Europe and the Mediterranean, and even as far as the northern reaches of the Black Sea.
View of the sanctuary at Delphi
The new drive turned out to be a determining factor in the history of the Celtic world, and involved an eastward shift in its center of gravity. This came about because of a consolidation of Celtic power throughout the middle Danube region from the second half of the fourth century B.C. By then, Celtic groups had reached the Illyrian regions further south, and collected their first resounding military victory in the Balkans with the crushing defeat of the Autariati. There is good reason to believe that the "Adriatic" Celts who made up the group of envoys sent to Alexander the Great (as mentioned in classical sources) were not in fact Gauls from Italy but Celts originating from the Pannonian hinterland, who provided a kind of springboard for the Gaulish invasion of the Hellenistic world.
In the last decade of the fourth century B.C., the Celtic thrust increased in intensity throughout the northeast of the Balkans. As quoted in Justinus, Pompeius Trogus gives a very clear idea of the chronology of events. From his account we learn that their settlement in Pannonia and the wars waged against neighboring peoples were followed by incursions on the Macedonians and Greeks. However, Celtic expansion was eventually contained in Thrace by Alexander the Great's successors, initially Cassander and then Lysimachus. After Alexander's death in the battle of Kouroupedion at the start of 281 B.C., the "Macedonian barrier" ceased to be effective and the way for Celtic penetration into the Greek heartland was thrown open.
Due to the loss of almost all historical records from the third century B.C., the more recent sources, such as Justinus's summary or the succinct outline left by Pausanias, written in Imperial times, give a very patchy and even confusing account of the Celtic invasion. Details are lacking on operations carried out by the Celtic forces, and there is no chronology of events.
We can reasonably assume that the offensive of 280 B.C. was three-pronged. The Celtic penetration of Triballi territory and Thrace was led by Kérethrios, while Illyria and Macedonia were invaded by Bolgios's warriors, and Peonia by troops under Brennus and Akichorios. The decisive blow was delivered by Bolgios's army which, early in 279 B.C., wiped out what remained of the forces of the young Macedonian sovereign, Ptolemy Ceraunus. The Galatians, as the Celts were more often called, took the wounded king prisoner and beheaded him. Their next move was nothing short of astonishing; having sealed their victory, the troops and their leader Bolgios simply withdrew to the land from which they had launched their attack. The unbarred way into Greece was an open invitation, however, and soon enough Brennus led his troops toward the south. Their progress was not without setbacks. According to Livy, in Dardania Leonnorios and Lutarios together with about twenty-thousand men left the main body of the army after a rebellion. Then, in Macedonia the troops of Brennus and Akichorios seem to have suffered heavy losses. Once beyond Thermopylae, Brennus and an elite corps of his finest warriors closed in on Delphi, whose fame had long spread outside the Greek world. But although the ancient sanctuary of Apollo suddenly found itself in a dreadful plight, the Celtic assault came to nothing. Tradition tells of a miracle worked by Apollo, and that Delphi was sacked and its treasures removed to Gaul. In reality, the rites of the soteri, introduced in Delphi shortly after the repulsion of the Celts, commemorated the liberation and the salvation of the sanctuary. Brennus himself was gravely wounded and, after success- fully seeing his troops join up with those of Akichorios, took his own life. Akichorios in turn opted for a withdrawal of troops toward Thrace. Their fate is unknown. The army of Kérethrios, the third group involved in the Greek offensive, can be defined as the force defeated by Antigonos Gonatos in 278-277 B.C. at Lysimacheia. Thus ended the Celts' great invasion of Greece. From then on, the only Galatians to be found there were mercenaries. The fundamental problem posed by the events briefly described above is exactly how should