The Holy Apostolic and Catholic Assyrian Church of the East is a Christian church that traces its origins to the See of Babylon, said to be founded by Saint Thomas the Apostle. In India, it is known as the Chaldean Syrian Church. In the West it is often known, inaccurately, as the Nestorian Church. The Assyrian Church is the original Christian church in what was once Parthia; today Iraq and western Iran. Geographically it stretched in the medieval period to China and India: a monument found in Xi'an (Hsi-an), the Tang-period capital of China (originally Chang'an), in Chinese and Syriac described the activities of the church in the 7th and 8th century, while half a millennium later the Chinese monk Rabban Bar Sauma went from Beijing to Paris and Rome to call for a crusade with the Mongols against the Mamelukes. Prior to the Portuguese arrival in India in 1498, it provided "East Syrian" bishops to the Saint Thomas Christians.