Tibetans became familiar with the mandala early in their introduction to Buddhist art and culture, a process begun with the first ruler of the historical period, Songtsen Gampo (srong-btsan sgam-po, d. 649). Mandalas existed at early Buddhist centers in central Asia, e.g. Dunhuang and Khotan, both frequented by Tibetans during the eighth and ninth centuries.17 Sketches of mandalas are found in the eighth through tenth century Dunhuang manuscripts which are among Tibet's earliest written records.18 Samye (bsam-yas), Tibet's first monastery founded ca. 779, was based on the architectural principles of a three-dimensional mandala, reportedly following the plan of Uddandapura monastery in eastern India.
Tibetan paintings on cloth (thang-ka) dating as early as the eleventh or twelfth centuries feature highly complex mandalas. Mandalas adorned the murals at early Tibetan sanctuaries, including Tabo (ta-pho, founded late tenth century; its murals dating probably to mid-eleventh century), and Alchi (al-chi, founded ca. 1200). At Sakya (sa-skya) monastery, extensive cycles of mandalas were painted between 1280 and 1305.19 Also adorned with ambitious cycles of mandalas are Shalu (zha-lu, founded ca. mid-eleventh century; mandalas dating to ca. early fourteenth century), and Gyantse (rgyan-rtse, completed ca. 1435). Founded ca. 1429 but destroyed, Ngor monastery was for centuries associated with magnificent painted mandalas, unsurpassed in iconographic complexity and aesthetic achievement.20
Much of the mandala's iconography and its associated liturgy are contained in texts known as tantras. Etymologically, tantra signifies a process of weaving or bringing together, reference to the process by which an individual undergoes psychic transformations, eventually leading to full enlightenment. Earlier Mahayana Buddhist literature had emphasized the bodhisattva, one who strove to assist others in the attainment of enlightenment and whose religious career was often described as prajnaparamita, "the perfection of wisdom," for it involved the cultivation - over many lifetimes - of wisdom, compassion, generosity, and similar qualities. Tantric texts, in contrast, promise spiritual liberation in this very life or in a few lifetimes, through highly sophisticated yoga practices.
This rapid spiritual ascent requires the guidance of one who has him or herself experienced the subtle terrain of the highest spiritual states. Tantric Buddhism thus places great emphasis on the teacher (guru, bla-ma). Teachings are tailored to the individual and often appear incomprehensible to the uninitiated, thus the appellation frequently associated with this phase of Buddhism, esoteric. Esoteric literature is necessarily associated with a strong oral tradition, one's teacher elucidating the obscure prose and ensuring that the disciple is morally, intellectually and spiritually prepared to receive its teachings.21
Many such texts, crucial to the identification and interpretation of the mandala, were translated into Tibetan from Sanskrit and can be found in a portion of the Tibetan Buddhist canon known as the Tanjur (bstan-'gyur).22 Tibet's extensive inheritance of Buddhist Sanskrit literature came under the scrutiny of successive Tibetan theologians. Sonam Tsemo (bsod-nams rtse-mo, 1142-1182) proposed a system of classification based upon the difficulty of practice contained within.23 Later, Buton Rinpoche (bu-ston rin-po-che, 1290-1364) deepened and strengthened this classification, which divides tantric literature into four main groups known as kriyatantra (bya-ba'i rgyud "action"), caryatantra (spyod-pa'i rgyud "performance"), yogatantra (rnal-'byor rgyud "yoga"), and anuttarayogatantra (rnal-'byor bla-na-med-pa'i rgyud "unsurpassed yoga"). Each main category was subdivided further, based on distinctions unique to each category.