In 1612, James I instructed Sir Thomas Roe to visit the Mughal Emperor Nuruddin Salim Jahangir (r. 1605 – 1627) to arrange for a commercial treaty that would give the Company exclusive rights to reside and build factories in Surat and other areas. In return, the Company offered to provide the Emperor with goods and rarities from the European market. This mission was highly successful as Jahangir sent a letter to James through Sir Thomas Roe:^[9]

"Upon which assurance of your royal love I have given my general command to all the kingdoms and ports of my dominions to receive all the merchants of the English nation as the subjects of my friend; that in what place soever they choose to live, they may have free liberty without any restraint; and at what port soever they shall arrive, that neither Portugal nor any other shall dare to molest their quiet; and in what city soever they shall have residence, I have commanded all my governors and captains to give them freedom answerable to their own desires; to sell, buy, and to transport into their country at their pleasure.
For confirmation of our love and friendship, I desire your Majesty to command your merchants to bring in their ships of all sorts of rarities and rich goods fit for my palace; and that you be pleased to send me your royal letters by every opportunity, that I may rejoice in your health and prosperous affairs; that our friendship may be interchanged and eternal"

—Nuruddin Salim Jahangir, Letter to James I.

The first Catholic missionaries who came to Siam were probably the chaplains of Portuguese ships in the 16th century sent to Ayutthaya bringing the officers of Portugal to enter into relations with Siam. There are no documents to confirm this hypothesis. There is a written history prepared by foreigners stating that in 1544, Antonio de Paiva, a Portuguese, had traveled to Ayutthaya in the time of Phra Jairaja and had been given an audience and had conversation about religion with the King. The King was converted and baptized, being given the Portuguese name of Dom Joâo. There is no evidence to confirm this claim. The first missionary who mentioned Siam in writings about his missionary task was St. Francis Xavier himself. He mentioned Siam in his four letters written from Sancian, although his real purpose was to go to China. However, St. Francis Xavier did not go either to China or to Siam because he died on December 3, 1552. .