The mountains of Northern Vietnam are home to a large number of the 54 different ethnic groups that give Vietnam the largest and most complex ethnic minority of Southeast Asia. The Tay and Thai are the dominant, formerly feudal, societies who hold the valley bottom land. The Hmong and Dzao people who arrived at the end of the 18th century have had to live and farm the least hospitable land at the highest altitudes; they preserve their traditional customs living at near-subsistence levels. Weekly local markets fulfill an important role in social and economic life.