Muslim invaders drove out Indian scholars to Tibet
Muslim invaders destroyed Buddhist monasteries of Udandapura and Vikramasila (In Bihar region) around 1200 CE. Many of the monks were killed and others fled to various countries. The learned Sakyasri went to Orissa and afterwards to Tibet; Ratnarakshita to Nepal;Buddamitra and others sought refuge in South India, While Sangama Srijnana with several of his followers went to Burma and Cambodia. And Buddhism became extinct in Magadha (modern Bihar).
Many emigrants from Magadha rejoined their brethren in the South and founded colleges in Vijayanagara, Kalinga and Konkan. The comparatively satisfactory condition of Buddhism in the Deccan about that time is attested by the rich donations to the monastery at Dambal.
Monks of the monasteries Udandapura and Vikramasila on their dispersion carried with them their arts and learning in the same manner as the Byzantine Greeks on their expulsion from Constantinople bore with them their intellectual treasures to the Italian cities. In the kingdom of Deccan and in Tibet the Buddhist refugees found hospitable asylums, just as the Greek philosophers found in the Florentine Republic under the Medici.
Tantric mysticism and alchemy were taught at the Universities of Nalanda, Udandapura and Vikramasila in Maghada and Central India and from thence it spread to Bhot ( Tibet) and to South India.
The Tantras found a home in China. Amoghavagra, a Brahmin converted to Buddhism, resided in China between 746 and 771 CE. He spread the science of supernatural powers, Siddhis, there.
Tibetan scriptures Kanjur (Kang- Gyur-The Translaation of the Word)) and Tanjur (Stan-ghyur-The Translation of the Treatises) ) were the Tibetan equivalent of Buddhist Tripitaka. Both represent an immense collection of works (108+224 Volumes) primarily translated from the Sanskrit and subsidiarily from the Chinese languages between the 7th and the13th centuries . These collections are of considerable value as most of their Sanskrit originals are either lost or now unavailable. The faithful accuracy of these translations and their fidelity to the original enable us often to reproduce the Sanskrit texts and thus provide us valuable historical data.
Tanjur, though a commentary of Kanjur (108 volumes) , is twice as large as the former and consists generally of 225 large volumes. Some parts of Tanjur are believed to date back to the seventh century, though the major portion was composed later. It is divided into two main classes Rgyud, corresponding to the Sanskrit Tantra and Mdo, corresponding to Sanskrit Sutra (Science and Literature).
MEDICINE, ASTROLOGY & ASTRONOMY
Some five volumes of Tanjur are devoted to medicine and some others to astronomy or astrology. We are indebted to a great Hungarian scholar Csoma de Koros for his pioneering work on the study of these two famous encyclopaedic Tibetan scriptures. In his analysis of the contents of the Mdo, Csoma has mentioned a work on preparing quick silver, (mercury) described as the most powerful agent for subduing every sickness and for improving the vigorous of the body, as well as a work on turning base metals into gold.
Pandit Vidhusekhar Bhattacharya, in his article on Sanskrit Treatises on Alchemy as translated into Tibetan has discussed about four works and given more information. He gave the Sanskrit names of four treatises as
1.Rasa siddhi sastra
Some of these works are translated into English.
The original Sanskrit texts of these works belong to eighth or ninth centuries. They are completely lost and fully depend upon Tibetan aand Chinese translation.
Rasa means mercury or quicksilver and Rasayana means Alchemy.