The Tibeto-Burman-speaking Pyu entered the Irrawaddy valley from present-day Yunnan, c. 2nd century BCE, and went on to found city states throughout the Irrawaddy valley. The original home of the Pyu is reconstructed to be Kokonor Lake in present-day Qinghai and Gansu provinces. The Pyu were the earliest inhabitants of Burma of whom records are extant. During this period, Burma was part of an overland trade route from China to India. Trade with India brought Buddhism from southern India. By the 4th century, many in the Irrawaddy valley had converted to Buddhism. Of the many city-states, the largest and most important was Sri Ksetra, southeast of modern Prome (Pyay). In March 638, the Pyu of Sri Ksetra launched a new calendar that later became the Burmese calendar.
Eighth century Chinese records identify 18 Pyu states throughout the Irrawaddy valley, and describe the Pyu as a humane and peaceful people to whom war was virtually unknown and who wore silk cotton instead of actually silk so that they would not have to kill silk worms. The Chinese records also report that the Pyu knew how to make astronomical calculations, and that many Pyu boys entered the monastic life at seven to the age of 20.
It was a long-lasting civilization that lasted nearly a millennium to early 9th century until a new group of "swift horsemen" from the north, the Mranma, (Burmans) entered the upper Irrawaddy valley. In the early 9th century, the Pyu city states of Upper Burma came under constant attacks by the Nanzhao Kingdom in present-day Yunnan. In 832, the Nanzhao sacked then Halingyi, which had overtaken Prome as the chief Pyu city state. A subsequent Nanzhao invasion in 835 further devastated Pyu city states in Upper Burma. While Pyu settlements remained in Upper Burma until the advent of the Pagan Empire in mid 11th century, the Pyu gradually were absorbed into the expanding Burman kingdom of Pagan in the next four centuries. The Pyu language still existed until the late 12th century. By the 13th century, the Pyu had assumed the Burman ethnicity. The histories/legends of the Pyu were also incorporated to those of the Burmans.