Pyu city states were a group of city-states that existed from c. 2nd century BCE to c. mid-11th century CE in present-day Upper Burma (Myanmar). The city-states were founded as part of the southward migration by the Tibeto-Burman-speaking Pyu, the earliest inhabitants of Burma of whom records are extant.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 city-states—five major walled cities and several smaller towns have been excavated—were all located in the three main irrigated regions of Upper Burma: the Mu valley, the Kyaukse plains and Minbu region, around the confluence of the Irrawaddy and Chindwin rivers. Part of an overland trade route between China and India, the Pyu realm gradually expanded south. Halin, founded in the 1st century CE at the northern edge of Upper Burma, was the largest and most important city until around the 7th or 8th century when it was superseded by Sri Ksetra (near modern Pyay) at the southern edge. Twice as large as Halin, Sri Ksetra was the largest and most influential Pyu center. The Pyu culture was heavily influenced by trade with India, importing Buddhism as well as other cultural, architectural and political concepts, which would have an enduring influence on later Burmese culture and political organization.[3] The Pyu calendar, based on the Buddhist calendar, later became the Burmese calendar. Latest scholarship, though yet not settled, suggests that the Pyu script, based on the Indian Brahmi script, may have been the source of the Burmese script. The millennium-old civilization came crashing down in the 9th century when the city-states were destroyed by repeated invasions from the Kingdom of Nanzhao. The Mranma (Burmans), who came down with the Nanzhao, set up a garrison town at Pagan (Bagan) at the confluence of Irrawaddy and Chindwin. Pyu settlements remained in Upper Burma for the next three centuries but the Pyu gradually were absorbed into the expanding Pagan Empire. 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.