The Pyu city states were a group of city-states that existed from about the 2nd century BCE to the mid-11th century in present-day Upper Burma (Myanmar). The city-states were founded as part of the southward migration by the Tibeto-Burman-speaking Pyu people, the earliest inhabitants of Burma of whom records are extant.^[8] The thousand-year period, often referred to as the Pyu millennium, linked the Bronze Age to the beginning of the classical states period when the Pagan Kingdom emerged in the late 9th century.

The 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 Qinghai Lake in present-day Qinghai and Gansu.^[9] The Pyu were the earliest inhabitants of Burma of whom records are extant.^[10] During this period, Burma was part of an overland trade route from China to India. Trade with India brought Buddhism from South India, as well as other cultural, architectural and political concepts, which would have an enduring influence on the political organisation and culture of Burma. By the 4th century, many in the Irrawaddy valley had converted to Buddhism.^[11] The Pyu script, based on the Brahmi script, may have been the source of the Burmese script used to write the Burmese language.^[12] Of the many city-states, the largest and most important was the Sri Ksetra Kingdom southeast of modern Pyay, also thought to once be the capital city.^[13] In March 638, the Pyu of Sri Ksetra launched a new calendar that later became the Burmese calendar.^[10]

The major Pyu city-states were all located in the three main irrigated regions of Upper Burma: the Mu River Valley, the Kyaukse plains and Minbu region, around the confluence of the Irrawaddy and Chindwin Rivers. Five major walled cities- Beikthano, Maingmaw, Binnaka, Hanlin, and Sri Ksetra - and several smaller towns have been excavated throughout the Irrawaddy River basin. Hanlin, founded in the 1st century CE, was the largest and most important city until around the 7th or 8th century when it was superseded by Sri Ksetra (near modern Pyay) at the southern edge of the Pyu Realm. Twice as large as Halin, Sri Ksetra was eventually the largest and most influential Pyu centre.^[10]

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 silkworms. 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.^[10]

It was a long-lasting civilisation that lasted nearly a millennium to the early 9th century until a new group of "swift horsemen" from the north, the Bamars, entered the upper Irrawaddy valley. In the early 9th century, the Pyu city-states of Upper Burma came under constant attacks by Nanzhao (in modern Yunnan). In 832, the Nanzhao sacked Halingyi, which had overtaken Prome as the chief Pyu city-state and informal capital.

The Bamar people set up a garrison town at Bagan (Pagan) at the confluence of the Irrawaddy and Chindwin Rivers. Pyu settlements remained in Upper Burma for the next three centuries but the Pyu gradually were absorbed into the expanding Pagan Kingdom. The Pyu language still existed until the late 12th century. By the 13th century, the Pyu had assumed the Burman ethnicity. The histories and legends of the Pyu were also incorporated to those of the Bamar.^[14]