Plato may therefore be regarded as the source of speculative mysticism in Europe, but it is Plotinus, his disciple, the Neo-platonist, who is the father of European mysticism in its full sense, practical as well as speculative, and who is also its most profound exponent. Plotinus (A.D. 204-270), who was an Egyptian by birth, lived and studied under Ammonius Sakkas in Alexandria at a time when it was the centre of the intellectual world, seething with speculation and schools, teachers and philosophies of all kinds, Platonic and Oriental, Egyptian and Christian. Later, from the age of forty, he taught in Rome, where he was surrounded by many eager adherents. He drew the form of his thought both from Plato and from Hermetic philosophy (his conception of Emanation), but its real inspiration was his own experience, for his biographer Porphyry has recorded that during the six years he lived with Plotinus the latter attained four times to ecstatic union with "the One." Plotinus combined, in unusual measure, the intellect of the metaphysician with the temperament of the great psychic, so that he was able to analyse with the most precise dialectic, experiences which in most cases paralyse the tongue and blind the discursive reason. His sixth Ennead, "On the Good or the One," is one of the great philosophic treatises of the world, and it sums up in matchless words the whole mystic position and experience. There are two statements in it which contain the centre of the writer's thought. "God is not external to any one, but is present in all things, though they are ignorant that he is so." "God is not in a certain place, but wherever anything is able to come into contact with him there he is present" (_Enn._ vi. 9, §§ 4, 7). It is because of our ignorance of the indwelling of God that our life is discordant, for it is clashing with its own inmost principle. We do not know ourselves. If we did, we would know that the way home to God lies within ourselves. "A soul that knows itself must know that the proper direction of its energy is not outwards in a straight line, but round a centre which is within it" (_Enn._ vi. 9, § 8).