A myriarchy unit in the Mongol-Yuan Sakya rule in Tibet in the thirteenth and fourteenth centuries was a highi level administrative unit in the decimal based system that constituted the administrative rule and divisions of the Mongol Yuan Empire’s rule in Tibet in conjunction with their Tibetan Sakya sect religious partners from 1268 to 1354. The term is defined as ten chiliarchies, or ten thousand households; the Tibetan term "trikor" literally means "ten thousand fold." The myriarchies in turn were organized into circuits, which were ten myriarchies. According to Petech (1979, p, 234), ideally a myriarchy was supposed to “contain 4000 temple serfs, 6000 serfs of noble families”.

Please see the parent feature type on the Sakya-Mongol Yuan State for an overview of the decimal-based scheme of administrative units in which the myriarchy units were positioned.

In addition, while the full scheme only existed in Tibet from 1268 to 1354,  the myriarchies continued to function after that as principalities. The various political periods in Central Tibet following 1354 are in fact named after whichever one of the myriarchies would temporarily go into political and military ascendancy to become functionally a kingdom dominating its former peers. Sorenson-Hazod-Gyalbo (2007) is a marvelous study of one such myriarchy, the Tshelpa (tshal pa), and offers great insight into the actual realities of such polities/political units

Per Sorenson and Guntram Hazod with Tsering Gyalbo (2007). Rulers on the Celestial Plain Ecclesiastic and Secular Hegemony in Medieval Tibet: A Study of Tshal Gung-thang. Austrian Academy of Sciences.This is the  best source on this system in Tibet.  See particularly appendix three on the Tshal pa khri 'khor. In addition, their footnotes on the mi sde of the tshal pa khri 'khor is probably the most detailed discussion of administrative/land units within an actual khri 'khor.

Luciano Petech. Central Tibet and the Mongols. The Yüan - Sa-skya Period of Tibetan History. Serie Orientale Roma LXV. Roma: Istituto per il Medio ed Estremo Oriente. V. 167 pp. This supercedes the earlier article by Petech cited below.

Luciano Petech. “The Mongol Census in Tibet.” In Tibetan Studies in Honour of Hugh Richardson: Proceedings of the International Seminar on Tibetan Studies, Oxford, 1979. Michael Aris and Aung San Suu Kyi, eds. Warminster, England: Aris & Phillips; Forest Grove, 1980. 233–238, and see in particular p. 234.