From this point it becomes necessary to vary the treatment of our subject hitherto followed. With the breakup of the Roman Empire and the establishment of Christianity the old learning was obliterated. Religion became the central fact of intellectual exercise, and, except in so far as Christian doctrine and Holy Scripture involved reference to natural phenomena, every branch of natural science was withered by the breath of theology. The first serious assaults of the barbarian invader were made on the frontiers of the Roman Empire in the fourth century A.D.; in 330 the seat of government was transferred from Rome to Byzantium, and at the close of the century the empire was divided into eastern and western parts. It has often been pointed out that these events did more than mark the beginning of the disruption of the Roman Empire; they also mark the parting of the ways of eastern and western European religion and culture. In the west it became the function of Christianity to teach and civilize peoples untaught and uncivilized; but, limited and intolerant as was its outlook upon natural science generally, it discarded the learning of the pre-Christian era. We have now to inquire how geography was affected by this attitude towards secular learning. It is true that the habit of travel, so far from being forgotten, was even fostered by missionary work and the practice of pilgrimage. Again, opportunities for the extension of geographical knowledge were provided by various episodes in the history of the centuries with which we are now concerned; thus Procopius, the historian of the Persian, Vandal, and Gothic wars of the epoch of the Roman (Byzantine) emperor Justinian in the sixth century, had ample opportunities for geographical description and used them well. Justinian even despatched an expedition to China (which returned thence). But the geographical theorists of the period now under review had little if any concern with contemporary travellers’ results.