Notwithstanding the traditional belief that disciples of Jesus Christ introduced Christianity into China, conclusive evidence showed that it was the Nestorian missionaries who entered China in AD 635. Alongside commercial contacts between the West and China during the prosperous T'ang dynasty (618-906), trepanation, bloodletting and the universal antidote theriac were introduced from the Byzantium Empire. Nestorian Christians built churches throughout China and offered some form of medical services. During the Yuan (Mongol) dynasty (1260-1368), foreign physicians were present in the Royal Court; the most famous was the astronomer, linguist and physician Ai-hsieh (Isaiah), Head of the Imperial Medical Bureau. With the fall of this dynasty, Christianity, being primarily the faith of a foreign community, naturally fell into oblivion. It was not until the sixteenth-century's Age of Discovery when a safe sea route to China was found that a new phase of Christian missionaries began.