It is in the practice of Plato as a teacher that we can most fitly consider the conception which the Greek philosophers in general had concerning the method of studying and imparting philosophy altogether. It was about the fortieth year of his life, and twelve years after the death of his master Socrates, that Plato, having already travelled widely, settled at Athens.(383) Here he purchased a fixed residence at the Academia, which became from that time a philosophical school for study, conversation, oral lectures, and friendly meetings. Here he drew around him an inner circle of scholars to whom he addressed his unwritten doctrines,(384) especially his doctrine of Ideas, the key to his whole system, according as they were able, after preparation, to receive them: and here besides he gave lectures which might be attended not only by that inner circle of choice disciples but by studious persons in general. This residence of Plato served for three hundred years, from 387 before Christ until the siege of Athens by Sylla in 87, as the centre of Plato’s philosophy viewed as a teaching power. Now in this Plato had before him the great example of Pythagoras, in the first age of Greek philosophy. Concerning the doctrines of that philosopher we know little with certainty,(385) but all are agreed as to his manner of teaching them. His attempt was to establish a community which should carry in its bosom, propagate, and perpetuate a doctrine in morals, politics, religion, and philosophy. His whole procedure was by oral teaching, for he left not a word written. It was in fact a religious order of life which he first practised in his own person, and then endeavoured to communicate to others. Into this order trial for everyone preceded reception.(386) His scholars were for a long period required to practise silent obedience and unconditional submission to the authority of the doctrine delivered to them. Severe daily examination was imposed upon all. The publishing of his doctrine, especially his speculation as to the nature of God, was strictly forbidden. The upright life, the learning which then could only be attained by personal inquiry, the persuasiveness of Pythagoras, were together so effective that he succeeded in establishing such a community both in Crotona and in other cities of Southern Italy. It was persecuted and suffered continual disasters, but still this Pythagorean community, bearing on its founder’s doctrines and manner of life, existed for several generations after his death, during which many of the most distinguished Greeks belonged to it. Such was the poet Æschylus, whose mind was formed on Pythagorean principles. In Plato’s time the Pythagorean Archytas was at the head of the state of Tarentum: and Plato himself was largely imbued with Pythagorean tenets.(387)