While Cato was engaged in this great work of forming his son's character and completing his education he found him eager to learn, and able to make great progress from his natural ability: but he appeared so weak and delicate that his father was obliged to relax the stern simplicity of his own life in his favour, and allow him some indulgences in diet. The young man, although so weakly, yet proved himself a good soldier in the wars, and distinfuished himself greatly in the battle in which Æmilius Paulus defeated King Perseus. Afterwards, upon the same day, he either had his sword struck from his hand or let it fall from weakness, and in his grief at the loss got together some of his friends and prevailed upon them again to charge the enemy. With great exertions they succeeded in clearing a space, and at length discovered his sword under a great heap of arms and corpses of friends and foes alike which were piled upon it. Paulus, the commander-in-chief, was much pleased with the youth's eagerness to regain his sword, and sent a letter to Cato in which he spoke in the highest terms of the courage and honourable feeling which he had shown. He afterwards married Tertia, the sister of Scipio, and had the gratification of pleasing his father as much as himself by thus allying himself with one of the noblest families in Rome. Thus was Cato rewarded for the care which he had bestowed upon his son's education. XXI. He possessed a large number of slaves, and when captives were for sale he always purchased those who were young, and who, like colts or puppies, could be taught and trained to their duties. None of them ever entered any house but his own, unless sent thither by Cato or by his wife: and if they were asked what Cato was doing, they always answered that they did not know. His rule was, that a slave ought either to be doing his business or to be asleep; and he greatly preferred good sleepers, as he thought that they were more easy tempered than wakeful persons, and also that men who had slept well were better able to work than those who had lain awake. Knowing that love affairs lead slaves into mischief more than anything else, he permitted them to consort with his own female slaves at a fixed price, but forbade them to have anything to do with other women.