The first instance of France-Thailand contacts is also the first historical record of an attempt to introduce Christianity to Siam: according to Giovanni Pietro Maffei, about 1550 a French Franciscan, Bonferre, hearing of the great kingdom of the Bagoans and the Thai in the east, went on a Portuguese ship from Goa to Cosme , where for three years he preached the gospel without any result. The first major contacts between the two countries occurred after Thailand was made an apostolic vicariate by Pope Alexander VII on 22 August 1662. The mission was assigned to the newly formed Paris Foreign Missions Society to evangelize Asia, and Siam became the first country to receive these efforts, to be followed by new missions 40 years later in Cochinchina, Tonkin and parts of China, because Siam was highly tolerant of other religions and was indeed the only country in Southeast Asia where the Catholic Fathers could establish themselves safely. Monseigneur Pierre Lambert de la Motte, Bishop of Beirut, Vicar-Apostolic of Cochinchina, and member of the Missions Etrangères de Paris, accompanied by Fathers De Bourges and Deydier, left Marseille on 26 November 1660, and reached Mergui 18 months later. He arrived in the Ayutthaya Kingdom in 1662.

When did Monseigneur Pierre Lambert de la Motte reach Mergui?
1661-February-26