The causes of this transformation were two-fold, internal or Indian and external.  Buddhism was a living, that is changing, stream of thought and the Hindus as a nation have an exceptional taste and capacity for metaphysics.  This taste was not destroyed by Gotama’s dicta as to the limits of profitable knowledge nor did new deities arouse hostility because they were not mentioned in the ancient scriptures.  The development of Brahmanism and Buddhism was parallel:  if an attractive novelty appeared in one, something like it was soon provided by the other.  Thus the Bhagavad-gita contains the ideas of the Mahayana in substance, though in a different setting:  it praises disinterested activity and insists on faith.  It is clear that at this period all Indian thought and not merely Buddhism was vivified and transmuted by two great currents of feeling demanding, the one a more emotional morality the other more personal and more sympathetic deities.

I shall show in more detail below that most Mahayanist doctrines, though apparently new, have their roots in old Indian ideas.  But the presence of foreign influences is not to be disputed and there is no difficulty in accounting for them.  Gandhara was a Persian province from 530 to 330 B.C. and in the succeeding centuries the north-western parts of India experienced the invasions and settlements of numerous aliens, such as Greeks from the Hellenistic kingdoms which arose after Alexander’s expedition, Parthians, Sakas and Kushans.  Such immigrants, even if they had no culture of their own, at least transported culture, just as the Turks introduced Islam into Europe.  Thus whatever ideas were prevalent in Persia, in the Hellenistic kingdoms, or in Central Asia may also have been prevalent in north-western India, where was situated the university town of Taxila frequently mentioned in the Jatakas as a seat of Buddhist learning.  The foreigners who entered India adopted Indian religions[14] and probably Buddhism more often than Hinduism, for it was at that time predominant and disposed to evangelize without raising difficulties as to caste.

Foreign influences stimulated mythology and imagery.  In the reliefs of Asoka’s time, the image of the Buddha never appears, and, as in the earliest Christian art, the intention of the sculptors is to illustrate an edifying narrative rather than to provide an object of worship.  But in the Gandharan sculptures, which are a branch of Graeco-Roman art, he is habitually represented by a figure modelled on the conventional type of Apollo.  The gods of India were not derived from Greece but they were stereotyped under the influence of western art to this extent that familiarity with such figures as Apollo and Pallas encouraged the Hindus to represent their gods and heroes in human or quasi-human shapes.  The influence of Greece on Indian religion was not profound:  it did not affect the architecture or ritual of temples and still less thought or doctrine.  But when Indian religion and especially Buddhism passed into the hands of men accustomed to Greek statuary, the inclination to venerate definite personalities having definite shapes was strengthened[15].