The use and manufacture of bronze drums is the oldest continuous art tradition in Southeast Asia. It began some time before the 6th century BC in northern Vietnam and later spread to other areas such as Burma, Thailand, Indonesia and China. The Karen adopted the use of bronze drums at some time prior to their 8th century migration from Yunnan into Burma where they settled and continue to live in the low mountains along the Burma - Thailand border. During a long period of adoption and transfer, the drum type was progressively altered from that found in northern Vietnam (Dong Son or Heger Type I) to produce a separate Karen type (Heger Type III). In 1904, Franz Heger developed a categorization for the four types of bronze drums found in Southeast Asia that is still in use today.