He was wonderfully fond of his father Antigonus; and the tenderness he had for his mother led him, for her sake, to redouble attentions, which it was evident were not so much owing to fear or duty as to the more powerful motives of inclination. It is reported that, returning one day from hunting, he went immediately into the apartment of Antigonus, who was conversing with some ambassadors, and after stepping up and kissing his father, he sat down by him, just as he was, still holding in his hand the javelins which he had brought with him. Whereupon Antigonus, who had just dismissed the ambassadors with their answer, called out in a loud voice to them, as they were going, "Mention, also, that this is the way in which we two live together;" as if to imply to them that it was no slender mark of the power and security of his government that there was so perfect good understanding between himself and his son. Such an unsociable, solitary thing is power, and so much of jealousy and distrust in it, that the first and greatest of the successors of Alexander could make it a thing of glory in that he was not so afraid of his son as to forbid his standing beside him with a weapon in his hand. And, in fact, among all the successors of Alexander, that of Antigonus was the only house which, for many descents, was exempted from crime of this kind; or to state it exactly, Philip was the only one of this family who was guilty of a son's death. All the other families, we may fairly say, afforded frequent examples of fathers who brought their children, husbands their wives, children their mothers, to untimely ends; and that brothers should put brothers to death was assumed, like the postulate of mathematicians as the common and recognized royal first principle of safety.
Let us here record an example in the early life of Demetrius, showing his natural humane and kindly disposition. It was an adventure which passed betwixt him and Mithridates, the son of Ariobarzanes, who was about the same age with Demetrius, and lived with him, in attendance on Antigonus; and although nothing was said or could be said to his reproach, he fell under suspicion, in consequence of a dream which Antigonus had. Antigonus thought himself in a fair and spacious field, where he sowed golden seed, and saw presently a golden crop come up; of which, however, looking presently again, he saw nothing remain but the stubble, without the ears. And as he stood by in anger and vexation, he heard some voices saying Mithridates had cut the golden harvest and carried it off into Pontus. Antigonus, much discomposed with his dream, first bound his son, by an oath not to speak, and then related it to him, adding that he had resolved, in consequence, to lose no time in ridding himself of Mithridates, and making away with him. Demetrius was extremely distressed; and when the young man came, as usual, to pass his time with him, to keep his oath he forbore from saying a word, but, drawing him aside little by little from the company, as soon as they were by themselves, without opening his lips, with the point of his javelin he traced before him the words "Fly, Mithridates." Mithridates took the hint, and fled by night into Cappadocia, where Antigonus's dream about him was quickly brought to its due fulfillment; for he got possession of a large and fertile territory; and from him descended the line of the kings of Pontus, which, in the eighth generation, was reduced by the Romans.
This may serve for a specimen of the early goodness and love of justice that was part of Demetrius's natural character.
But as in the elements of the world, Empedocles tells us, out of liking and dislike, there springs up contention and warfare, and all the more, the closer the contact, or the nearer the approach of the objects, even so the perpetual hostilities among the successors of Alexander were aggravated and inflamed, in particular cases, by juxtaposition of interests and of territories; as, for example, in the case of Antigonus and Ptolemy. News came to Antigonus that Ptolemy had crossed from Cyprus and invaded Syria, and was ravaging the country and reducing the cities. Remaining, therefore, himself in Phrygia, he sent Demetrius, now twenty-two years old, to make his first essay as sole commander in an important charge. He, whose youthful heat outran his experience, advancing against an adversary trained in Alexander's school, and practised in many encounters, incurred a great defeat near the town of Gaza, in which eight thousand of his men were taken and five thousand killed. His own tent, also his money, and all his private effects and furniture, were captured. These, however, Ptolemy sent back, together with his friends, accompanying them with the humane and courteous message, that they were not fighting for anything else but honour and dominion. Demetrius accepted the gift praying only to the gods not to leave him long in Ptolemy's debt, but to let him have an early chance of doing the like to him. He took his disaster, also, with the temper, not of a boy defeated in his attempt, but of an old and long-tried general familiar with reverse of fortune; he busied himself in collecting his men, replenishing his magazines, watching the allegiance of the cities, and drilling his new recruits.
Antigonus received the news of the battle with the remark that Ptolemy had beaten boys and would now have to fight with men. But not to humble the spirit of his son, he acceded to his request, and left him to command on the next occasion.