Of the irruption of the Galati into Greece I gave some account in connection with the council-chamber at Athens: but I prefer to give the fullest account in connection with Delphi, because the greatest struggle between them and the Greeks took place here. The first expedition of the Celts beyond their borders was under Cambaules: but when they got as far as Thrace on that occasion they did not dare to go any further, recognising that they were too few in number to cope with the Greeks. But on the second expedition, egged on by those who had formed part of the army of Cambaules, who had tasted the sweets of plunder and were enamoured of the gains of looting, a large army of both infantry and cavalry mustered together. This army the commanders divided into three parts, and each marched into a different district. Cerethrius was to march against the Thracians and the Triballi: Brennus and Acichorius were to lead their division into Pæonia: and Bolgius was to march against the Macedonians and Illyrians. This last fought a battle against Ptolemy king of the Macedonians, who had treacherously slain Seleucus the son of Antiochus, (though he had been a suppliant at his court), and was nicknamed Lightning on account of his audacity.[109] In this battle Ptolemy fell, and with him no small part of the Macedonians: but the Celts durst not adventure any further into Greece, and so this second expedition returned home again. Thereupon Brennus urgently pressed upon the general assemblies, and upon each individual chieftain of the Galati, the advantages of invading Greece, pointing out her weak state at that period, and the immense wealth of her community, her votive offerings in the temples, her quantity of silver and gold. He succeeded in persuading the Galati to invade Greece once more, and among other chieftains he chose Acichorius once more as his colleague. The army mustered 152,000 foot and 20,400 horse. Such at least was the fighting force of the cavalry, for its real number was 61,200: as each horse-soldier had two servants, who themselves were excellent cavalry also and mounted. For the custom of the Galati in an engagement was that these servants should remain in the rear close at hand, and if a horse was killed they supplied a fresh one, and if the rider was killed one of them took his place, and if he too was killed then the third took his place. And if one of the masters was only wounded, then one of his servants removed him to the camp, and the other took his place in the battle. In this custom I think the Galati imitated the 10,000 Persians, called _The Immortals_. But the difference was that _The Immortals_ were a reserve force only used at the end of an action, whereas the Galati used these reserves as wanted all through the action. This mode of fighting they called _Trimarcisia_ in their dialect: for the Celts called a horse _marca_. Such was the force, such the intentions, with which Brennus marched into Greece.