André de Longjumeau

André de Longjumeau (also known as Andrew of Longjumeau in English) was a 13th-century Dominican missionary and diplomat and one of the most active Occidental diplomats in the East in the 13th century. He led two embassies to the Mongols: the first carried letters from Pope Innocent IV and the second bore gifts and letters from Louis IX of France to Güyük Khan. Well acquainted with the Middle-East, he spoke Arabic and "Chaldean" (thought to be either Syriac or Persian).[1]

Mission for the holy Crown of Thorns

Andrew went to Constantinople to obtain the Crown of Thorns bought by Louis IX from Baldwin II. It is preserved today in a 19th-century reliquary, in Notre-Dame Cathedral, Paris.

Andrew's first mission to the East was when he was asked by the French king Louis IX to go and fetch the Crown of Thorns which had been sold to him by the Latin Emperor of Constantinople Baldwin II in 1238, who was anxious to obtain support for his tottering empire.[1] Andrew was accompanied on this mission by brother Jacques.