Although Tibet is geographically closer to India, Buddhism reached that country many centuries after its arrival in east Asia. This is due to a combination of geographical and economic reasons. Tibet is the highest country in the world located on a vast plateau occupying over 1.5 million square miles surrounded by high mountains. For a country the size of western Europe, it has a tiny population, estimated at some 6 million in the present century. Isolated between the economically and culturally advanced civilizations of India andChina.Tibet had few readily accessible natural resources and only a subsistence economy, so there were few trade missions or caravans for monks to attach themselves to. It was thus not until the 7th century ce that Buddhism made an appearance. Traditional chronicles speak of three ‘diffusions’ of Buddhism, the first of which begins with Songtsen Gampo (Tib., Srong bstan sgam po, ca. 618–50), the first of the three ‘religious kings’. This king had a Nepalese and a Chinese wife, both of whom brought Buddhist artefacts with them to Tibet. The second ‘religious king’ was Trisong Detsen (Tib., Khri srong lde brtsan), who invited the scholar-monk Śāntarakṣita from India to promulgate Buddhist teachings. The latter made little progress, and withdrew in favour of Padmasambhava, a tantric guru and popular Tibetan folk hero. It is said that through his magical powers Padmasambhava was able to overcome the demons who were obstructing Buddhism's progress in Tibet. These ‘demons’ can, perhaps, be identified with practitioners of the indigenous Bön religion, a form of central Asian shamanism which imprinted something of its distinctive character, including an interest in rites, rituals, and magical practices surrounding death.on Buddhism. With the ‘demons’ subdued and the way clear, Śāntarakṣita returned to Tibet, and with Padmasambhava co-founded the first monastery at Samyé (bsam yas) c.767 ce. Another important missionary to arrive in this period was Kamalaśīla, who played a decisive role in ensuring that Tibetan Buddhism developed along Indian rather than Chinese lines. The third ‘religious king’, Relpa Chen (Tib., Ral pa can, r. 815–36), continued the construction of temples and monasteries and as a result of royal patronage the ranks of the Saṃgha began to swell. This led to a backlash against Buddhism and Relpa Chen was assassinated in 836 and succeeded by Lang Darma (Tib., glang dar ma), a king less favourably disposed to Buddhism, who was himself subsequently assassinated by a Buddhist monk. The arrival of Atiśa (982–1054) from India in 1042 marks the start of the second diffusion. Atiśa laid emphasis on the conventional monastic curriculum, but his disciples also included more colourful individuals who became known as Mahāsiddhas or ‘great adepts’. Chief among these tantric gurus are Marpa (1012–97), Milarepa (Tib., Mi la ras pa, 1040–1123), and Gampopa (Tib., sgam po pa, 1079–1153). Gampopa established this lineage as a monastic order known as the Kagyüpa (Tib., bka' brygud pa). Two further orders were established during the high medieval period, the Sakyapa (Tib., Sa skya pa) and the Gelukpa (Tib., dge lugs pa). The latter, a reform movement founded by Tsongkhapa (Tib., Tsong kha pa, 1357–1419), went on to become the most influential in both the spiritual and temporal spheres, effectively ruling Tibet from the 17th century through the office of the Dalai Lama. Together with the Nyingma pa (Tib., rnying ma pa), who trace their origins to Padmasambhava, these constitute the four main orders of Tibetan Buddhism.