The broad, fertile plains of Central Thailand form the traditional heartland of old Siam, as they have since the Thai capital moved south from Sukhothai to Ayuthaya in the mid-14th century. Central Thailand, dominated by Bangkok, is the political powerhouse of the country. It provides the national language - Thai - which is spoken throughout the kingdom and understood everywhere, even by those whose first language is a regional dialect (such as the Northern Thai people) or a distinct minority language (as in the hill tribes).