It was these relations who kept the army together when he lay a captive in the Castel dell'Uovo at Naples; his sister took the royal envoys prisoners with her own hands, and saved him by this reprisal from death. It was an indication of the breadth and the range of his plans that in monetary affairs Jacopo was thoroughly trustworthy: even in his defeats he consequently found credit with the bankers. He habitually protected the peasants against the license of his troops, and reluctantly destroyed or injured a conquered city. He gave his well-known mistress, Lucia, the mother of Francesco, in marriage to another, in order to be free for a princely alliance. Even the marriages of his relations were arranged on a definite plan. He kept clear of the impious and profligate life of his contemporaries, and brought up his son Francesco to the three rules: 'Let other men's wives alone; strike none of your followers, or, if you do, send the injured man far away; don't ride a hard-mouthed horse, or one that drops his shoe.' But his chief source of influence lay in the qualities, if not of a great general, at least of a great soldier. His frame was powerful, and developed by every kind of exercise; his peasant's face and frank manners won general popularity; his memory was marvelous, and after the lapse of years could recall the names of his followers, the number of their horses, and the amount of their pay. His education was purely Italian: he devoted his leisure to the study of history, and had Greek and Latin authors translated for his use. Francesco, his still more famous son, set his mind from the first on founding a powerful State, and through brilliant generalship and a faithlessness which hesitated at nothing, got possession of the great city of Milan (1450).