(M678) It was at this time, B.C. 387, that Plato visited Sicily on a voyage of inquiry and curiosity, chiefly to see Mount Ætna, and was introduced to Dion, then a young man in Syracuse, and brother-in-law to Dionysius. Dion was so impressed with the conversation of Plato, that he invited the tyrant to talk with him also. Plato discoursed on virtue and justice, showing that happiness belonged only to the virtuous, and that despots could not lay claim even to the merit of true courage—most unpalatable doctrine to the tyrant, who became bitterly hostile to the philosopher. He even caused Plato to be exposed in the market as a slave, and sold for twenty minæ, which his friends paid and released him. On his voyage home, through the influence of the tyrant, he was again sold at Egina, and again repurchased, and set at liberty. So bitter are tyrants of the virtues which contrast with their misdeeds; and so vindictive especially was the despot who reigned at Syracuse. (M679) Dionysius was now occupied, by the new defenses and fortifications of his capital, so that the whole slope of Epipolæ was bordered and protected by massive walls and towers, and five divisions of the city had each its separate fortifications, so that it was the largest fortified city in all Greece—larger than Athens herself. (M680) The plunder the tyrant had accumulated enabled him to make new preparations for a war with Carthage. But he was defeated in a great battle at Cronium, with terrible loss, by the youthful son of Magon, which compelled him to make peace, and cede to Carthage all the territory of Sicily west of the river Halycus, and pay a tribute of one thousand talents.