Plutarch Pyrrhus 11

[1] Such letters the kings kept sending to Pyrrhus, and at the same time on their own part they assailed Demetrius while he was still waiting to complete his preparations. Ptolemy sailed up with a great fleet and tried to bring the Greek cities to revolt, while Lysimachus invaded upper Macedonia from Thrace and ravaged the country. So Pyrrhus, taking the field at the same time with these, marched against Beroea, expecting, as proved to be the case, that Demetrius would go to confront Lysimachus, and thus leave the lower country unprotected.

[2] That night Pyrrhus dreamed that he was called by Alexander the Great, and that when he answered the call he found the king lying on a couch, but met with kindly speech and friendly treatment from him, and received a promise of his ready aid and help. And how, O King, Pyrrhus ventured to ask, when thou art sick, canst thou give me aid and help? My name itself will give it, said the king, and mounting a Nisaean horse he led the way.

[3]
  This vision gave Pyrrhus great assurance, and leading his army with all speed through the intervening districts he took possession of Beroea; then, stationing the greater part of his forces there, he proceeded to subdue the rest of the country through his generals. When Demetrius heard of this, and became aware of a pernicious uproar in his camp on the part of the Macedonians, he was afraid to lead them farther on, lest on coming into the neighbourhood of a Macedonian king of great renown they should go over to him.

[4] Therefore he turned back and led them against Pyrrhus, with the idea that he was a foreigner and hated by the Macedonians. But after he had pitched his camp over against Pyrrhus, many Beroeans came thither with loud praises of Pyrrhus; they said he was invincible in arms and a brilliant hero, and treated his captives with mildness and humanity. There were some also whom Pyrrhus himself sent into the camp; they pretended to be Macedonians, and said that now was the favourable time to rid themselves of Demetrius and his severity, by going over to Pyrrhus, a man who was gracious to the common folk and fond of his soldiers.

[5] In consequence of this, the greater part of the army was all excitement, and went about looking for Pyrrhus; for it chanced that he had taken off his helmet, and he was not recognised until he bethought himself and put it on again, when its towering crest and its goat’s horns made him known to all. Some of the Macedonians therefore ran to him and asked him for his watchword, and others put garlands of oaken boughs about their heads because they saw the soldiers about him garlanded.

[6] And presently even to Demetrius himself certain persons ventured to say that if he quietly withdrew and renounced his undertakings men would think that he had taken wise counsel. He saw that this advice tallied with the agitation in the camp, and was frightened, and secretly stole away, after putting on a broad-brimmed hat and a simple soldier’s cloak. So Pyrrhus came up, took the camp without a blow, and was proclaimed king of Macedonia.