When the great King Anawrahta of Pagan united the whole of Burma into a single kingdom in the eleventh century and made Theravada Buddhism the national religion, there were already in existence a number of primitive religious cults, the most important and the most popular of which were the worship of ''Nat" spirits, astrology, and alchemy. In addition, there were also Mahayana Buddhism and Tantric (or magical) Buddhism, but debased and distorted, and bearing strange fruit from the fertile soil of native cults of magic and sorcery. All the different cults were given an artificial unity by the fact that they were all under the patronage of the Ari monks. These Ari monks had some acquaintance with the Buddhist scriptures, gloried in the name of the Buddha, and wore dark brown robes and conical hats. But they also presided over the Nat spirit festivals, at which hundreds of animals were sacrificed.
Astrology to the Burmese meant not only the methods of tracing the courses of the planets and their influence on mortals, but also the ritual by which the planets were appeased and made to withdraw their baneful influence. In other words, it involved a worship of the planets. As Burmese astrology had its origins in Hindu astrology, the worship of the planets also involved worship of at least some of the Hindu gods.
Alchemy also came to Burma from India, but Burmese alchemy became a religious cult. The Burmese alchemist did not merely seek the power to transmute base metals into gold, but had the noble aim of evolving an eternally youthful body, which would be an answer to the perpetual human lament that beauty and youth must pass.
The worship of Nats was purely native in origin, and developed out of that form of animism which still prevails among some of the hill peoples of the country. The term "Nat" originally meant a "lord," and involved an idea similar to feudal overlordship. A Nat was a spirit who had some dominion over a group of people or over a certain object or objects. The spirit who had dominion over a small withered tree was as much a Nat as the spirit who had dominion over a particular village or district. The suzerainty of a Nat was both territorial and personal. The Nat guardian of a village had power over all those who were born in the village or born of a village family, wherever they might be, and he also had power over all who came to his village, during the time they remained there. He would inflict no harm, nay, he would even give his protection, to those who recognized his suzerainty, and such recognition could be expressed by an offering of rice or fruit, or by a few words of supplication, or a gesture of homage.
At first the Nats that were worshiped were impersonal and local, as for example, the Nats of the banyan tree, the hill, and the lake which were just outside the village, and the guardian Nat of the village. Later on, thirty-six personal and national Nats came into being, who were distinct personages with their own life histories, and who were worshiped all over the country. They did not replace the local Nats, but diminished their importance.
The most important of the thirty-six were the Lord of the Great Mountain, and his sister Lady Golden-Face, whose abode was on Mount Popa, an extinct volcano in central Burma. They became, in the ninth century, the guardian gods of the city of Pagan and its kings. There was an annual Nat feast on Mount Popa itself, at which hundreds of animals were offered as sacrifice to the Lord of the Great Mountain and Lady Golden-Face. People came from afar to take part in the feast, to get drunk with ecstasy and toddy wine, and to dance with abandon, believing themselves to have become possessed by the Nats. There were spirit mediums in attendance at the Nat shrines, who provided the wild music and led the wilder dances. The Popa feast was held on a full moon day in December, and on other full moon days there were also feasts connected with other pre-Buddhist cults.