Task: Question Answering
Input (English): Passage: The Eastern Han general Ban Chao (32–102 AD), in a series of military successes which brought the Western Regions (the Tarim Basin of Xinjiang) back under Chinese control and suzerainty, defeated the Da Yuezhi in 90 AD and the Northern Xiongnu in 91 AD, forcing the submission of city-states such as Kucha and Turfan, Khotan and Kashgar (Indo-European Tocharian and Saka settlements, respectively), and finally Karasahr in 94 AD. An embassy from the Parthian Empire had earlier arrived at the Han court in 89 AD and, while Ban was stationed with his army in Khotan, another Parthian embassy came in 101 AD, this time bringing exotic gifts such as ostriches.In 97 AD, Ban Chao sent an envoy named Gan Ying to explore the far west. Gan made his way from the Tarim Basin to Parthia and reached the Persian Gulf. Gan left a detailed account of western countries; he apparently reached as far as Mesopotamia, then under the control of the Parthian Empire. He intended to sail to the Roman Empire, but was discouraged when told that the trip was dangerous and could take two years. Deterred, he returned to China bringing much new information on the countries to the west of Chinese-controlled territories, as far as the Mediterranean Basin.Gan Ying is thought to have left an account of the Roman Empire (Daqin in Chinese) which relied on secondary sources—likely sailors in the ports which he visited. The Book of the Later Han locates it in Haixi ("west of the sea", or Roman Egypt; the sea is the one known to the Greeks and Romans as the Erythraean Sea, which included the Persian Gulf, the Arabian Sea, and Red Sea):
Its territory extends for several thousands of li  [a li during the Han dynasty equalled 415.8 metres]. They have established postal relays at intervals, which are all plastered and whitewashed. There are pines and cypresses, as well as trees and plants of all kinds.  It has more than four hundred walled towns. There are several tens of smaller dependent kingdoms. The walls of the towns are made of stone.
The Book of the Later Han gives a positive, if inaccurate, view of Roman governance:
Their kings are not permanent rulers, but they appoint men of merit. When a severe calamity visits the country, or untimely rain-storms, the king is deposed and replaced by another. The one relieved from his duties submits to his degradation without a murmur. The inhabitants of that country are tall and well-proportioned, somewhat like the Han [Chinese], whence they are called [Daqin]. 
Question: What is the full name of the empire in which the Book of the Later Han states, "kings are not permanent rulers, but they appoint men of merit"?
Output (English): Roman Empire.