He soon had many rivals and enemies in the field against him. The three principal ones were Antiochus, Antigonus, and Pyrrhus. Antiochus was the son of Seleucus. He maintained that his father had fairly conquered the kingdom of Macedon, and had acquired the right to reign over it; that Ptolemy Ceraunus, by assassinating Seleucus, had not divested him of any of his rights, but that they all descended unimpaired to his son, and that he himself, therefore, was the true king of Macedon. Antigonus was the son of Demetrius, who had reigned in Macedon at a former period, before Lysimachus had invaded and conquered the kingdom. Antigonus therefore maintained that his right was superior to that of Ptolemy, for his father had been the acknowledged sovereign of the country at a period subsequent to that of the reign of Antipater. Pyrrhus was the third claimant. He had held Macedon by conquest immediately before the reign of Lysimachus, and now, since Lysimachus had been deposed, his rights, as he alleged, revived. In a word, there were four competitors for the throne, each urging claims compounded of rights of conquest and of inheritance, so complicated and so involved, one with the other, as to render all attempts at a peaceable adjudication of them absolutely hopeless. There could be no possible way of determining who was best entitled to the throne in such a case. The only question, therefore, that remained was, who was best able to take and keep it.
This question Ptolemy Ceraunus had first to try with Antigonus, who came to invade the country with a fleet and an army from Greece. After a very short but violent contest, Antigonus was defeated, both by sea and by land, and Ceraunus remained master of the kingdom. This triumph greatly strengthened his power in respect to the other competitors. He, in fact, contrived to settle the question with them by treaty, in which they acknowledged him as king. In the case of Pyrrhus, he agreed, in consideration of being allowed peaceably to retain possession of his kingdom, to furnish a certain amount of military aid to strengthen the hands of Pyrrhus in the wars in which he was then engaged in Italy and Sicily. The force which he thus furnished consisted of five thousand foot, four thousand horse, and fifty elephants.