The Pagan kingdom, also known as the Pagan dynasty, 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.