Diadochi ("successors"): name of the first generation of military and political leaders after the death of the Macedonian king and conqueror Alexander the Great in 323 BCE. To settle the question whether his empire should disintegrate or survive as a unity, and, if so, under whose rule, they fought several full-scale wars. The result, reached by 300, BCE, was a division into three large parts, which more or less coincided with Alexander's possessions in Europe, Asia, and Egypt.
During the next quarter of a century, it was decided whether these states could endure. As it turned out, there were no great territorial changes, although there were dynastic changes. After 280, the period of state-forming came to an end with three great states: Antigonid Macedonia, Ptolemaic Egypt, and the Seleucid kingdom in Asia.
The kingdom of Lysimachus had been a kind of buffer zone between on the one hand the civilized world of Greece and Asia and on the other hand the Thracian tribes of the north. The king had known how to cope with the barbarians: he had understood that, when one tribe became dangerous, he had to negotiate with its neighbors - in other words, during the almost forty years of his reign, he had learned to maintain a balance of power in what is now Bulgaria and Serbia.
But Lysimachus had been killed during the battle of Corupedium, and his successor Seleucus, who had learned the same game in dealing with the Sacae in Central-Asia, had been murdered a few months later. His official successor was Antiochus, who had spent much time in the eastern satrapies and knew how to deal with the tribes as well. But the man who succeeded Seleucus in Europe knew nothing of customs of the 'barbarians': Ptolemy Keraunos, who had been educated in Egypt. And there was no time to learn it, because he was confronted with a larger threat than Lysimachus, Seleucus or Antiochus had ever had to cope with.The Galatians had arrived in northern Bulgaria.
The Galatians belonged to the La Tène-culture, which had its heartland in northeastern France and southern Germany. In the fifth and fourth centuries, it had expanded to the west into the countries where people spoke a language that modern scholars call 'Celtic'. Because the Greeks used the word 'Celt' to describe all barbarians in the west (except for the inhabitants of the British isles), twentieth-century scholars have used the word 'Celtic' to describe all La Tène-people, even when they did not live in the west and did not speak a Celtic language. Therefore, the Galatians are sometimes called Celts, which is in fact incorrect but has the advantage that people immediately understand that the Galatians were savages.
Ptolemy Keraunos was no match for them. When the well-known Thracian tribes asked for his help, he refused, thinking that if they were weakened by the invaders, they were less dangerous to his new kingdom (281). Instead, they now had to join forces with the Galatians. In the spring of 279, their leader Bolgius invaded Macedonia, and when Keraunos offered battle, he was captured and decapitated.
For two years, Macedonia had no central government: three men were offered the crown, but two of them were immediately dethroned and the third one, a nobleman named Sosthenes, refused the supreme power. The cities had to help themselves. Fortunately, the Galatians were unable to besiege towns, so that city-dwellers were safe. Sosthenes was able to harass Bolgius, who returned to Serbia with his loot.
This encouraged another leader, who is called Brennus in our sources (in fact, brennus seems to have been the word for 'duke'). Because the Macedonia countryside was now empty, he decided to invade Greece in 279/278 (text). When he reached Thermopylae, however, he was forced to fight against a coalition of warriors from free Greek towns and soldiers of king Antigonus II Gonatas. But the pass of Thermopylae was turned and Brennus could invade central Greece. He decided to raid Delphi and seems to have entered the sanctuary. But a thunderstorm and early snow forced him to return. The Galatians suffered heavy losses and Brennus committed suicide, and the Greeks thought that the god Apollo had defeated the Galatians in person.
At the same time, a third group of Galatians invaded Thrace. They were very successful and were even able to cross to Asia. Thrace was now in a state of anarchy and in 277, Antigonus Gonatas decided to capture its capital Lysimachia on the Hellespont. When he was approaching, he encountered a group of Galatians, and he defeated them. This gave him sufficient credit to become king of Thrace and Macedonia.
This was the end of the Galatian invasion. Its significance was that Macedonia had found a new king. From now on, Alexander's empire was divided into three parts with strong dynasties: the Seleucid empire in Asia, the Ptolemaic empire of Egypt and southern Syria, and Macedonia/Greece. Although they were sometimes at war with each other - the Ptolemies and the Seleucids fought several wars - they recognized each other. An equilibrium now existed, and remained intact for more than a century, when a new superpower entered the arena: Rome.
The only undefeated group of Galatians was the expeditionary force in Asia Minor. For some time, nobody dared to resist them, until Antiochus was able to defeat them with his elephants in 275 (for which he was called Soter, 'savior').