[Translated by Henry Graham Dakyns, The Education of Cyrus, New York, 1914. Translation amended by me.]
Book VII, Chapter 5
And so it came about that Cyrus entered the palace, and those in charge brought the treasures from Sardis thither, and handed them over. And Cyrus when he entered sacrificed to Hestia, the goddess of the Hearth, and to Zeus the Lord, and to any other gods named by the Persian priests.
58. This done, he set himself to regulate the matters that remained. Thinking over his position, and the attempt he was making to govern an enormous multitude, preparing at the same time to take up his abode in the greatest of all famous cities, but yet a city that was as hostile to him as a city could be, pondering all this, he concluded that he could not dispense with a bodyguard for himself. 59. He knew well enough that a man can most easily be assassinated at his meals, or in his bath, or in bed, or when he is asleep, and he asked himself who were most to be trusted of those he had about him. A man, he believed, can never be loyal or trustworthy who is likely to love another more than the one who requires his guardianship. 60. He knew that men with children, or wives, or favourites in whom they delight, must needs love them most: while eunuchs, who are deprived of all such dear ones, would surely make most account of him who could enrich them, or help them if they were injured, or crown them with honour. And in the conferring of such benefits he was disposed to think he could outbid the world. 61. Moreover the eunuch, being degraded in the eyes of other men, is driven to seek the assistance of some lord and master. Without some such protection there is not a man in the world who would not think he had the right to over-reach a eunuch: while there was every reason to suppose that the eunuch would be the most faithful of all servants. 62. As for the customary notion that the eunuch must be weak and cowardly, Cyrus was not disposed to accept it. He studied the indications to be observed in animals -- a vicious horse, if gelded, will cease to bite and be restive, but he will charge as gallantly as ever; a bull that has been cut will become less fierce and less intractable, but he will not lose his strength, he will be as good as ever for work; castration may cure a dog of deserting his master, but it will not ruin him as a watch-dog or spoil him for the chase. 63. So, too, with men; when deprived of this desire, they become gentler, no doubt, but not less quick to obey, not less daring as horsemen, not less skilful with the javelin, not less eager for honour. 64. In war and in the chase they show plainly enough that the fire of ambition is still burning in their hearts. And they have stood the last test of loyalty in the downfall of their masters. None have shown more faithfulness than eunuchs when ruin has fallen on their lords. 65. In bodily strength, perhaps, the eunuchs seem to be lacking, but steel is a great leveller, and makes the weak man equal to the strong in war. Holding this in mind, Cyrus resolved that his personal attendants, from his doorkeepers onward, should be eunuchs one and all.