The Mongols’ irruption into the Muslim empire all the more fired the imaginations since for the first time a significant part of the land of Islam eastward of Egypt was submitted to a non-Muslim rule. This foreign dominance has been symbolised in the medieval Islamic sources by the imposition of a Mongol law, the yasa (in classical Mongol language jasaq), a law perceived by the Muslims as opposite to the shari‘a. The Mongol law gave way to a long tradition of studies inaugurated by Pétis de la Croix (Histoire du grand Genghizcan, Paris, 1710). The latter launched the idea that Genghis Khan had promulgated in 1206 a written law code that he tried to reconstruct through the complilation of later Islamic sources; he relied in particular on the polemic testimony of al-Maqrizi (d. 1442), a prominent scholar of religious sciences of the Mamluk period. Silvestre de Sacy, by his translation and comment of this passage of al-Maqrizi, in 1826, also contributed to the overvaluation of this text as a source for the history of the Mongol law (Chrestomathie arabe ou Extrait de divers écrivains arabes, tant en prose qu’en vers, 2, Paris, 1826). This reconstructed code of the Mongol law emerged as a reference for the whole scientific community until D. Ayalon questioned the value of al-Maqrizi’s testimony in “The Great Yasa of Chingiz Khan: A Reexamination,” Studia islamica 33 (1971): 97-140 (part A: The Basic Data in the Islamic Sources on the Yasa an Its Content). None of these studies, however, has attempted to resituate the jasaq / yasa in the Mongol cultural context. Nor did they analyse the reasons why the Muslims considered this new Mongol order as contrary to Islam. Last, these successive contributions did not show very interested in the perception of the jasaq by the Mongols themselves.
In order to clarify this notion of jasaq / yasa the author of the present study the author has mobilised all the available sources (in Arabic, Latin, Mongol, Persian and Syriac languages). She has established the distinction between its strict meaning in Mongol language and its accepted sense among Muslim authors. In “The Secret History of the Mongols” the term jasaq is always employed with the meaning of the law of a ruler in the exercise of his power. The term yosun appears in the same text as a custom. According to Mongol sources the precepts of the jasaq did concern the affairs of the state, which is confirmed by Latin and Chinese sources. The jasaq was constituted by decrees and laws issued by the great qans in order to rule the Mongol Empire, and had no religious connotation of any sort. However the Muslims did perceive the jasaq / yasa as a code of laws like the shari‘a, which drove them to consider as yasa Mongol simple customary rules (yosun). Examining the yasa in its political and religious contexts, and taking into account the Mongols’ system of representations, the author explains the reasons of the misunderstanding by the Muslims of the Mongol customary laws, and shows that the latter were not imposed upon Muslim populations fallen under Mongol rule.