Pyrrhus had heard rumors of treason throughout the 470s. Initially, he had expected this to be mere unfounded gossip, but then he had noticed strange behavior among his courtiers, notably the Gelid family. This prompted him to investigate, and what he found stunned him. At first, he found nothing.
However, when he announced to his court what he intended to do with regards to Illyria, he found that his relative, Tryphon Aiakid, refused to support his plans of expansion. He claimed that invading such a vast land would be catastrophic, as the Diadochi would begin seeing Pyrrhus as a threat to their power. This made Pyrrhus suspicious, and he sent men to follow Tryphon - he worried that he could oppose his Illyrian Campaigns as the current Governor of Illyria. However, he didn’t have enough evidence that he was the type of man to do this, so he couldn’t fire his relative without harming his image among his subjects.
Interestingly, Pyrrhus quickly found a far more nefarious plot - Tryphon wasn’t loyal to Pyrrhus at all! It seemed as if he was plotting rebellion - either to take the throne of Epirus himself or, failing that, to become the king of an independent Illyrian state. This outraged Pyrrhus, who ordered Tryphon arrested.
Tryphon arrived for his trial, but things quickly went wrong. The head of the Gelid family vouched for Tryphon, and he demanded that Tryphon be found innocent. To make matters worse, the jury agreed with him. That might have been the end of the matter, but Tryphon’s honor had been injured. To make things even worse, Pyrrhus and Tryphon got into a scuffle and injured each other.
He declared war on Pyrrhus for his claim to Epirus as a member of the Aiakid family, and most of the Gelids joined him. Illyria and a city in Magna Graecia supported his claim. They began attacking Epirus itself.
Pyrrhus raised his armies, but he also hired mercenaries with his vast treasury. He didn’t fully trust his soldiers to be loyal to him above their commanders. The mercenaries, at the very least, would be loyal to whoever paid them. The practice of hiring mercenaries would be common throughout the history of Ancient Epirus - to their own eventual undoing.
Pyrrhus ordered his small army and his mercenaries to attack Illyria. At first, this left Epirus defenseless, so there was a risk of Pyrrhus himself being captured. He wasn’t that worried, though - he viewed Tryphon as too incompetent to manage that feat. Even if he was captured, he could always commit suicide and leave this fight to his descendants.
It didn’t come to that, as Pyrrhus is nowadays perhaps best known for his Illyrian Campaigns, which occurred after this civil war. In May 475, a siege of Apollonia began, but the walls proved too strong for the mercenaries ordered to besiege the city. They decided that dealing with the rebellion directly would be smarter than what they had been ordered to.
The mercenaries were right - the Battle of Passaron lasted all of one day. That day was January 26, 476, and 382 men of Korkyra were killed with the loss of 50 mercenaries. Korkyra’s support for the rebellion had been unknown to Pyrrhus, but, when the letter informing him of that fact arrived, he was angry. He decided that they needed to be punished for their treason, especially since it wasn’t even the first time that this had happened.
The mercenaries then began reclaiming the occupied areas of Epirus, and that task was completed by the end of May. This was followed by the Siege of Korkyra, which lasted from June 476 until May 477. It was only after this that Apollonia was besieged, and it finally fell in January 478.
In July, the last remnants of the forces of both Korkyra and the rebels were destroyed at the Battle of Lissos. This was followed by the fall of the city of Epidamnos in July 479, and the revolt was almost completely finished.
Parallel to the destruction of the rebellion’s armies was the destruction of the rebellion’s reputation. In June 476, Pyrrhus discovered that Archagathos Gelid was spreading insulting rumors about him, so he publicized this fact. He was then captured and executed, and he was stupid enough to admit his guilt to the court.
The war was finally completed once Pyrrhus simply outbid the mercenaries that the revolt was hiring for their service. That left Tryphon without any base of support, as they had been defending his territory in Magna Graecia, and he was executed.
Pyrrhus could now focus on conquering the northern tribes…