The Kingdom of Pagan (ပုဂံခေတ်, bəɡàɰ̃ khɪʔ, Pagan Period; also known as the Pagan dynasty and the Pagan Empire; also the Bagan dynasty or Bagan Empire) was the first Burmese kingdom to unify the regions that would later constitute modern-day Myanmar. Pagan's 250-year rule over the Irrawaddy valley and its periphery laid the foundation for the ascent of Burmese language and culture, the spread of Bamar ethnicity in Upper Myanmar, and the growth of Theravada Buddhism in Myanmar and in mainland Southeast Asia.
The kingdom grew out of a small 9th-century settlement at Pagan (present-day Bagan) by the Mranma/Burmans, who had recently entered the Irrawaddy valley from the Kingdom of Nanzhao. Over the next two hundred years, the small principality gradually grew to absorb its surrounding regions until the 1050s and 1060s when King Anawrahta founded the Pagan Empire, for the first time unifying under one polity the Irrawaddy valley and its periphery. By the late 12th century, Anawrahta's successors had extended their influence farther to the south into the upper Malay peninsula, to the east at least to the Salween river, in the farther north to below the current China border, and to the west, in northern Arakan and the Chin Hills. In the 12th and 13th centuries, Pagan, alongside the Khmer Empire, was one of two main empires in mainland Southeast Asia.
The Burmese language and culture gradually became dominant in the upper Irrawaddy valley, eclipsing the Pyu, Mon and Pali norms by the late 12th century. Theravada Buddhism slowly began to spread to the village level although Tantric, Mahayana, Brahmanic, and animist practices remained heavily entrenched at all social strata. Pagan's rulers built over 10,000 Buddhist temples in the Bagan Archaeological Zone of which over 2000 remain. The wealthy donated tax-free land to religious authorities.
The kingdom went into decline in the mid-13th century as the continuous growth of tax-free religious wealth by the 1280s had severely affected the crown's ability to retain the loyalty of courtiers and military servicemen.