In the intervals of his literary and didactic labours he twice visited Sicily; the first time at the invitation of his friend Dion, the relative and minister of the two Dionysii, the younger of whom had succeeded to his father’s throne, and whom Dion hoped to win to justice and moderation by the eloquent wisdom of the Athenian sage. Such hopes were doomed to bitter disappointment. His second visit to Syracuse was undertaken at the urgent entreaties of his Pythagorean friends, of whose tenets and dietetic principles he always remained an ardent admirer. For whatever reason, it proved unsuccessful. Dion was driven into exile, and Plato himself escaped only by the interposition of Archytas. Thus the only chance of attempting the realisation of his ideal of a communistic commonwealth--if he ever actually entertained the hope of realising it--was frustrated. Almost the only source of the biographies of Plato are the _Letters_ ascribed to him, commonly held to be fictitious, but maintained to be genuine by Grote. The narrative of the first visit to Sicily is found in the seventh Letter. We can refer but briefly to the nature of the philosophy and writings of Plato. In the notice of Pythagoras it has been stated that Plato valued very highly that teacher’s methods and principles. Pythagoreanism, in fact, enters very largely into the principal writings of the great disciple and exponent (and, it may safely be added, improver) of Sokrates, especially in the _Republic_ and the _Timæus_. The four cardinal virtues inculcated in the _Republic_--justice or righteousness (Δικαιοσύνη), temperance or self-control (Εγκρατεία or Σωφροσύνη), prudence or wisdom (Φρονήσις), fortitude (Ἀνδρεία)--are eminently pythagorean.