The sudden change in the condition of Don John might remind one of some fairy tale, where the poor peasant boy finds himself all at once converted by enchantment into a great prince. A wiser man than he might well have had his head turned by such a rapid revolution of the wheel of fortune; and Philip may naturally have feared that the idle dalliance of a court, to which his brother was now exposed, might corrupt his simple nature and seduce him from the honourable path of duty. Great, therefore, must have been his satisfaction, when he saw that, far from this, the elevation of the youth had only served to give a wider expansion to his views, and to fill his bosom with still higher and nobler aspirations. The discreet conduct of Don John in regard to his nephew, Don Carlos, when the latter would have engaged him in his wild and impracticable schemes, established him still more firmly in the royal favour.[148] In the spring of the year 1568, an opportunity occurred for Philip to gratify his brother's ambition, by entrusting him with the command of a fleet then fitting out, in the port of Carthagena, against the Barbary corsairs, who had been making alarming depredations of late on the Spanish commerce. But, while giving him this appointment, the king was careful to supply the lack of experience in his brother by naming as second in command an officer in whose abilities he perfectly confided. This was Antonio de Zuñiga y Requesens, grand commander of St. James, an eminent personage, who will come frequently before the reader in the progress of the narrative. Requesens, who at this time filled the post of ambassador at Rome, was possessed of the versatility of talent so important in an age when the same individual was often required to exchange the duties of the cabinet for those of the camp. While Don John appeared before the public as the captain of the fleet, the actual responsibility for the conduct of the expedition rested on his lieutenant. On the third of June, Don John sailed out of port, at the head of as brave an armament as ever floated on the waters of the Mediterranean. The prince's own vessel was a stately galley, gorgeously fitted up, and decorated with a profusion of paintings, the subjects of which, drawn chiefly from ancient history and mythology, were of didactic import, intended to convey some useful lesson to the young commander. The moral of each picture was expressed by some pithy maxim inscribed beneath it in Latin. Thus, to whatever quarter Don John turned his eyes, they were sure to fall on some homily for his instruction; so that his galley might be compared to a volume richly filled with illustrations, that serve to impress the contents on the reader's memory.[149]