After the fall of the Mongol Yuan Dynasty, the Ming Dynasty drove the few small Nestorian Christian communities in China underground and largely closed China off to foreigners. Only in the 16th century with the arrival of Portuguese traders did contacts with the West begin to be revived. The newly founded Jesuit order organized a mission to China led by Matteo Ricci. After finding his efforts at establishing a presence in the country stymied by the government, Ricci discovered that the key to securing a permanent Jesuit presence in China was his knowledge of Western astronomy.