Probable explanation.
Rage of Cambyses.

Prexaspes then said that he had no doubt that the two magians whom Cambyses had left in charge of the government had contrived to seize the throne. He reminded Cambyses that the name of one of them was Smerdis, and that probably that was the Smerdis who was usurping the supreme command. Cambyses said that he was convinced that this supposition was true. His dream, in which he had seen a vision of Smerdis, with his head reaching to the heavens, referred, he had no doubt, to the magian Smerdis, and not to his brother. He began bitterly to reproach himself for having caused his innocent brother to be put to death; but the remorse which he thus felt for his crime, in assassinating an imaginary rival, soon gave way to rage and resentment against the real usurper. He called for his horse, and began to mount him in hot haste, to give immediate orders, and make immediate preparations for marching to Susa.

Cambyses mortally wounded.

As he bounded into the saddle, with his mind in this state of reckless desperation, the sheath, by some accident or by some carelessness caused by his headlong haste, fell from his sword, and the naked point of the weapon pierced his thigh. The attendants took him from his horse, and conveyed him again to his tent. The wound, on examination, proved to be a very dangerous one, and the strong passions, the vexation, the disappointment, the impotent rage, which were agitating the mind of the patient, exerted an influence extremely unfavorable to recovery. Cambyses, terrified at the prospect of death, asked what was the name of the town where he was lying. They told him it was Ecbatane.

His remorse and despair.

He had never thought before of the possibility that there might be some other Ecbatane besides his splendid royal retreat in Media; but now, when he learned that was the name of the place where he was then encamped, he felt sure that his hour was come, and he was overwhelmed with remorse and despair.

He suffered, too, inconceivable pain and anguish from his wound. The sword had pierced to the bone, and the inflammation which had supervened was of the worst character. After some days, the acuteness of the agony which he at first endured passed gradually away, though the extent of the injury resulting from the wound was growing every day greater and more hopeless. The sufferer lay, pale, emaciated, and wretched, on his couch, his mind, in every interval of bodily agony, filling up the void with the more dreadful sufferings of horror and despair.

Cambyses calls his nobles about him.
His dying declaration.

At length, on the twentieth day after his wound had been received, he called the leading nobles of his court and officers of his army about his bedside, and said to them that he was about to die, and that he was compelled, by the calamity which had befallen him, to declare to them what he would otherwise have continued to keep concealed. The person who had usurped the throne under the name of Smerdis, he now said, was not, and could not be, his brother Smerdis, the son of Cyrus. He then proceeded to give them an account of the manner in which his fears in respect to his brother had been excited by his dream, and of the desperate remedy that he had resorted to in ordering him to be killed. He believed, he said, that the usurper was Smerdis the magian, whom he had left as one of the regents when he set out on his Egyptian campaign. He urged them, therefore, not to submit to his sway, but to go back to Media, and if they could not conquer him and put him down by open war, to destroy him by deceit and stratagem, or in any way whatever by which the end could be accomplished. Cambyses urged this with so much of the spirit of hatred and revenge beaming in his hollow and glassy eye as to show that sickness, pain, and the approach of death, which had made so total a change in the wretched sufferer's outward condition, had altered nothing within.

Death of Cambyses.