The introduction of Buddhism occurred in the seventh century A.D., when Tibetan king Srongtsen Gampo (reigned A.D. 627-49), a convert to Buddhism, ordered the construction of two Buddhist temples, at Bumthang in central Bhutan and at Kyichu in the Paro Valley. Buddhism replaced but did not eliminate the Bon religious practices that had also been prevalent in Tibet until the late sixth century. Instead, Buddhism absorbed Bon and its believers. As the country developed in its many fertile valleys, Buddhism matured and became a unifying element. It was Buddhist literature and chronicles that began the recorded history of Bhutan.
In A.D. 747, a Buddhist saint, Padmasambhava (known in Bhutan as Guru Rimpoche and sometimes referred to as the Second Buddha), came to Bhutan from India at the invitation of one of the numerous local kings. After reportedly subduing eight classes of demons and converting the king, Guru Rimpoche moved on to Tibet. Upon his return from Tibet, he oversaw the construction of new monasteries in the Paro Valley and set up his headquarters in Bumthang. According to tradition, he founded the Nyingmapa sect--also known as the "old sect" or Red Hat sect--of Mahayana Buddhism, which became for a time the dominant religion of Bhutan. Guru Rimpoche plays a great historical and religious role as the national patron saint who revealed the tantras--manuals describing forms of devotion to natural energy--to Bhutan. Following the guru's sojourn, Indian influence played a temporary role until increasing Tibetan migrations brought new cultural and religious contributions.
There was no central government during this period. Instead, small independent monarchies began to develop by the early ninth century. Each was ruled by a deb (king), some of whom claimed divine origins. The kingdom of Bumthang was the most prominent among these small entities. At the same time, Tibetan Buddhist monks (lam in Dzongkha, Bhutan's official national language) had firmly rooted their religion and culture in Bhutan, and members of joint Tibetan-Mongol military expeditions settled in fertile valleys. By the eleventh century, all of Bhutan was occupied by Tibetan-Mongol military forces.