V. As the elements, because of their mutual attraction and repulsion, are, according to Empedokles, always at variance with one another, and especially with those with which they happen to be in contact, so, while all the successors of Alexander were always at war, circumstances from time to time caused hostilities between two or more of them to take an especially active form. At this time Antigonus was at war with Ptolemy, and, hearing that Ptolemy had left the island of Cyprus, had landed in Syria and was ravaging that country, he himself remained in Phrygia, but sent his son Demetrius to oppose him. Demetrius was now two and twenty years of age, and was now for the first time entrusted with the sole management of an important campaign. As might be expected of so young and untried a commander, when pitted against a man trained to war under Alexander, and who had since his death waged many wars with success, Demetrius was defeated near the city of Gaza with a loss of fifteen thousand killed and eight thousand prisoners. He also lost his own tent, his property, and all his personal attendants. These, however, were restored to him, with all his captured friends, by Ptolemy, who sent him a kindly-worded message to the effect that they ought not to fight as mortal foes, but only for honour and empire. Demetrius, after receiving this message and his property, prayed to the gods that he might not long remain in Ptolemy's debt, but that he might soon recompense him in like manner. He did not behave himself like a youth who has received a check at the outset of his first campaign, but repaired his failure like an old and wary commander, enrolling fresh soldiers, providing new supplies of arms, keeping a firm hold over the cities near him and carefully drilling his new levies.