"[A]t least in Eastern Tibet, there existed during and after the time of Lha-tho-tho-ri [Fl.173(?)-300(?) CE] a solid knowledge of Buddhism and that the upper classes of the people were faithfully devoted to it. But the border regions in the north and west probably had also come into contact with Buddhism long before the time of Srong-btsan-sgam-po. Buddhist teachings reached China via a route along the western and northern borders of the Tibetan culture and language zone; the same route was travelled by Indian Pandits and Chinese pilgrims in their endeavour to bring this Indian religion to China. There used to be contacts with the Tibetan population in these border regions. It is possible that the knowledge gained from these encounters was spread by merchants over large areas of Tibet. Thus, when Srong-btsan-sgam-po succeeded to the throne of Tibet in the year 627, the country was ready for a systematic missionary drive under royal patronage."