Isa Tarsah Kelemechi (Mongolian: Isa Khelmerchi (Isa the Interpreter); Chinese: Ai-hsüeh) was an Assyrian Nestorian Christian scientist, and official at the Yuan court of Kublai Khan's Mongol Empire in the 13th century.
Astrologer in China
Isa Kelemechi was named head of the "Office of Western Astronomy" established by the Mongol ruler Kubilai Khan in 1263 to study Muslim astronomical observations. Kubilai would establish a second Observatory for Islamic astronomy in 1271, directed by astronomer Jamal al-Din.
Isa Kelemechi was also instrumental in reinforcing anti-Muslim prohibitions in the Mongol realms, such as prohibiting halal slaughter and circumcision, and, according to Rashid al-Din encouraged denunciation of Muslims. Isa Kelemechi also showed to Khubilai the Muslim precept of "Kill the polytheists, all of them", raising the suspicion of the Mongols towards Muslims. According to Rashid al-Din, as a result "most Muslims left Khitai".
Diplomat to Europe
Isa Kelemechi was later a member of the first mission to Europe sent by the Mongol Il-Khan ruler Arghun in 1285. He met with Pope Honorius IV, remitting a letter from Ghazan offering to "remove" the Saracens and divide "the land of Sham, namely Egypt" with the Franks. The message, written in imperfect Latin, said:
"And now let it be [says the Il-Khan], because the land of the Saracens is not ours, between us, good father, us who are on this side and you who are on your side; the land of Scami [Sham] to wit the land of Egypt between you and us we will crush. We send you the said messengers and [ask] you to send an expedition and army to the land of Egypt, and it shall be now that we from this side shall crush it between us with good men; and that you send us by a good man where you wish the aforesaid done. The Saracens from the midst of us we shall lift and the Lord Pope and the Cam [Great Khan Qubilai] will be lords".—Message from Arghun to Pope Honorius IV.
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