What was the source of the theology developed in the newer Sufism? Undoubtedly this was neo-Platonic, as has been proved by Dr. Nicholson (_Selected Poems from the Diwan of Shams-i-Tabriz_, Camb., 1898, and _The Mystics of Islam_, Lond. 1914), and by Prof. Browne (_Literary Hist. of Persia_, Lond., 1902, chap. xiii.), and forms part of the influence which came into Islam at the introduction of Greek philosophy under the `Abbasids. But as in philosophy and other cultural transmissions direct Greek influence was preceded by an indirect influence brought to bear through Syriac and Persian, so it was also in neo-platonic theology, for neo-Platonic influences had already been brought to bear upon the Syrians and Persians in the pre-Islamic period. In the forefront of the later direct influence must be placed the so-called _Theology of Aristotle_, which it is no exaggeration to describe as the most prominent and the widest circulated manual of neo-Platonism which has ever appeared. It is, as we have already stated, an abridged translation of the last three books of Plotinus’ _Enneads_. Now the mysticism of Plotinus is philosophical and not religious, but it lends itself to a theological interpretation very easily, just as neo-Platonism as a whole very readily became a theological system in the hands of Jamblichus, of the pagans of Harran, and such like; and the Sufis were inclined to make this application, whilst the _falasifa_ confined themselves to its philosophical side. It seems probable that the influence of the Pseudo-Dionysius was brought to bear upon Islam about the same time. The Pseudo-Dionysian writings consist of four treatises, of which two, a treatise “On Mystical Theology” in five chapters, and a treatise “On the Names of God” in thirteen chapters, have been the chief source of Christian mystical theology. The first reference to these writings occurs in A.D. 532, when the claim was made that they were the work of Dionysius, the Areopagite, a pupil of St. Paul, or at least represent his teaching. In several places the writer cites Hierotheus as his teacher, and this enables us to identify the source as a Syrian monk named Stephen Bar Sudaili, who wrote under the name of Hierotheus (cf. Asseman, _Bibl. Orient._ ii. 290-291). This Bar Sudaili was abbot of a convent at Edessa, and was involved in controversy with James of Sarugh, so that we may refer the writings to the latter part of the 5th century A.D. They were translated into Syriac very soon after their first appearance in Greek, and, as familiar to Syriac Christians, must have become indirectly known to the Muslims. We have no direct evidence as to their translation into Arabic, but Mai gives fragments of other works of Bar Sudaili which appear in Arabic MSS. in his _Spicilegium Romanum_ (iii. 707). The traditional view of the relations between Sufism and philosophy is described in the anecdote cited by Prof. Browne (_Lit. Hist. of Persia_, ii.