I hope you'll forgive me, I can provide most of my sources, but won't be able to quote directly as I'm on a different continent from them.

There's some rich debate among the Tibetan scholarly community over how much of Bon, what we now call the pre-Buddhist Tibetan religion, was a distinct religious tradition (or religious-tradition-complex). Christopher Beckwith in a footnote to Empires of the Silk Road goes so far to refer to any pre-Buddhist indigenous Tibetan as a "fiction" that "unfortunately persists," (I may be paraphrasing). Yet, there are religious leaders like Tsering Wangyal Rinpoche who claim to descend from a long line of Bonpo teachers.

The problem stems from (as it usually does) language and the lack of available sources. Tibetan history begins in the 630s with the invention of Tibetan language and the beginning of Tibetan historical sources. The first documents that can be called "history," (i.e. that aren't itemized lists of supplies, war materiel, and tribute) don't begin until the mid-late 700s and by then are mostly about which family and what leaders were responsible for helping bring Buddhism to Tibet (the Testament of Ba is probably the most famous, and extant, of these sources. So the Ba family often takes a starring role in early Tibetan history. Funny that...). There is even a misperception that Tibetan language was developed in order to translate Buddhist scripture from India, so at the very incception of any historical source that might help solve this issue, we have tainted sources and ideas.

The fact of the matter is that Tibetan language was developed mainly for state-building purposes. And Buddhism was brought to Tibet for the same reason. In the seventh and eighth centuries, Tibet was surrounded by Buddhist countries: Harsha and his Pala successors were patrons of the fabulous Nalanda monastery, the Sogdians were Manichaean but later Buddhist, the cities of the rich Silk Route(s) were all primary Buddhist trading and manuscript centers, Nepal was dominated by Buddhist kings, and T'ang China had a vibrant Buddhist community. It would make sense that Buddhism would have infiltrated into Tibet before the seventh century, even in a folk form, and we can make arguments for and against.

It's worth noting (Sam Van Schaik does an excellent job of describing the state of affairs in Tibetan Zen) that what we now think of as "Zen" (or Ch'an in China, Seon in Korea, or Dhyana in India) as a developed lineage, calmly descending into an upside-down tree of serene Buddhist masters, handing the mastery over their school, is very much a modern invention. At the time of Zen's dissemination in medieval Asia, it was more like an explosion of teachers and teachings, some of whom founded temples, monasteries, and lineages, and some of whom we know only fragments about. Documents in Tibetan (and Chinese, so I hear) will at times contain a random assortment of Zen teachers, in no particular order or relation to each other, and a small segment of their teachings. (See Tibetan Zen.) It would be only a hypothesis, but it would probably be more strange if no Buddhist teachers made it to Tibet prior to the eighth century. But that is in fact when the Buddhist story in Tibet officially begins.[1]

Tibetan history tells of three "Dharma kings" that served as Tibet's "great emperors." The first is Tri Songtsen Gampo. He is most famous for forcing the submission of the kings of Zhangzhung (to the west), Nepal, and 'Azha (to the east). The vassalization of Nepal was brought on when an exile king sought the safety of his court, and the emperor married Princess Balsa. He then returned his father-in-law to the Throne of Nepal. After the submission of the 'Azha [2] Tri Songtsen Gampo was married to Princess Kongjo (Wen'cheng in Chinese). The Nepali and the Chinese Princess were (in the Tibetan tradition) Bodhisattvas sent to help establish Buddhism in Tibet. Through Princess Balsa's knowledge of architecture, and Princess Kongjo's knowledge of geomancy (probably related to Yijing numerology, see Dickinson/Moore) the two Princess-Bodhisattvas laid the groundwork for Buddhism in Tibet.

Cont'd