This article begins by examining a newly released edict of Ming Ch'engtsu. This edict was issued on the ninth day of the second month in the eleventh year of the Yung-lo reign (1413) in which So-pa mgon dpon 1Ha btsan skyabs was conferred the ssu-t'u title. Based mainly on the data provided by a Tibetan religious historical work Shel dkar chos 'byung, this So-pa mgon dpon 1Ha btsan skyabs is identified as the descendant of La stod 1Ho khri dpon, one of the Thirteen Myriarchies (khri skor bcu gsum) in dBus and gTsang designated by the Mongol-Yuan court (1279-1368). This article provides new thoughts on the components, origins, developments and mutual relationships of the Thirteen Myriarchies in dBus and gTsang by exploring the history of La stod 1Ho khri skor. Furthermore, three other Tibetan ssu-t'u-Chang-pa headman Cha-pa, Pa-er local official So-nan-pa and Yang-si-tu-pa Kung-ko-pa, whose title were granted at the same time as that of 1Ha btsan skyabs-are identified as La stod Byang pa mgo dpon [rNam rhyal] grags pa, rTse chen nub pa bSod nams dpal and Nyang stod pa Kun dga' pa, respectively. An investigation of the history of these four headmen families reveals that certain members of all four families had been bestowed the ssu-t'u title by the Yuan court. Judging from the fact that the ssu-t'u title was indiscriminately granted during the later period of the Yuan dynasty, that almost every Tibetan Myriarch received the ssu-t'u title as a honorary rank, and that the rank of ssu-t'u did not exist in the Ming dynasty at all, the conferment of the ssu-t'u title specifically to the Tibetan headmen by Ming Ch'eng-tsu can only be understood as a continuation of the Yuan legacy in Tibet. In order words, Yuan practice in Tibet was the foundation for Ming policy toward Tibet.