Noted in the MSL from the 16th century as a polity under Yun-nan, Geng-ma was evidently ruled by a Tai nobility. It was centred on what is today Lan-cang Dai and Wa Nationality Autonomous County in Yun-nan, PRC. Alternate names include Keng-ma and Kaing-ma. For further details, see Mangrai (1981a).
For information on further Chinese sources relating to this polity, see Dao Yong-ming (1989; 269-70, 947), Fang Guo-yu (1987; 852, 875, 1071) and Gong Yin (1985; 128-129, 229-30 and 1992; 550-51).