Villages evolve into settled cultures and, by the middle of this period, stratified societies with centralized rule have developed on mainland Southeast Asia. The large drums produced by the Dongson culture in northern Vietnam are among the most distinctive artifacts of the period. Traders and religious missionaries come from India, and evidence of an early form of writing based on Sanskrit has been identified in Cambodia. Cultural links between southern Vietnam and island Southeast Asia continue to grow with the settlement of Austronesian speakers from Borneo. Around 111 B.C., Chinese conquerors first under the leadership of Emperor Wu and then General Ma Yuan gain control of Vietnam.