Stephen Carlson (former lawyer come NT student) has a post on Clement of Alexandria on Buddhism. I found this interesting because I was once studying various missionary movements in the Graeco-Roman world including Judaism and Christianity, but I also noticed that Christian authors were aware of the existence of Buddhist teachers and missionaries in places such as Egypt, Asia Minor and Britain. In fact, Elaine Pagels in her book Gnostic Gospels argued for the influence of Buddhism on Thomasine Christianity. Here a few citations that I have tracked down on the internet (I have not double checked the primary sources just yet).
Clement of Alexandria recognized the influence of Bactrian Buddhists (Sramanas) and Indian Gymnosophists on Greek thought: "Thus philosophy, a thing of the highest utility, flourished in antiquity among the barbarians, shedding its light over the nations. And afterwards it came to Greece. First in its ranks were the prophets of the Egyptians; and the Chaldeans among the Assyrians; and the Druids among the Gauls; and the Sramanas among the Bactrians ("Σαρμαναίοι Βάκτρων"); and the philosophers of the Celts; and the Magi of the Persians, who foretold the Saviour's birth, and came into the land of Judaea guided by a star. The Indian gymnosophists are also in the number, and the other barbarian philosophers. And of these there are two classes, some of them called Sramanas ("Σαρμάναι"), and others Brahmins ("Βραφμαναι")." (Strom 1.15).
Origen stated that Buddhists co-existed with Druids in pre-Christian Britain: "The island (Britain) has long been predisposed to it (Christianity) through the doctrines of the Druids and Buddhists, who had already inculcated the doctrine of the unity of the Godhead" (Commentary on Ezekiel).
Hippolytus knew of the Indian Brahmins and includes their tradition among the various sources of heresy: “There is . . . among the Indians a heresy of those who philosophize among the Brahmins, who live a self-sufficient life, abstaining from (eating) living creatures and all cooked food … They say that God is light, not like the light one sees, nor like the sun nor fire, but to them God is discourse, not that which finds expression in articulate sounds, but that of knowledge through which the secret mysteries of nature are perceived by the wise” (Adv. Haer).
Scythianus was an Alexandrian religious teacher who visited India around 50 CE. He is mentioned by several Christian writers of the 3rd and 4th centuries CE, including Cyril of Jerusalem, Hippolytus and Epiphanius. Cyril of Jerusalem says this of his pupil Terebinthus: “But Terebinthus, his disciple in this wicked error, inherited his money and books and heresy, and came to Palestine, and becoming known and condemned in Judaea he resolved to pass into Persia: but lest he should be recognised there also by his name he changed it and called himself Buddas." (Catechetical Lecture 6.23)
