The Roman occupation of Northern Iraq lasted less than a hundred and seventy years, from A.D. 197 to 364, and was little more than a turbulent episode in the long struggle between Rome on the west and Persia, under her successive Parthian and Sassanian rulers, on the east. The purely military character of this frontier extension is the first of the factors controlling the nature and distribution of its material remains; the second is the high degree of civilisation which the area had attained long before the Romans came, and was to maintain with little change long after their withdrawal. The process of Romanisation, if it was ever attempted, has left no mark. New towns would hardly have been built on sites already occupied by cities far older than Rome itself, and new roads were only constructed for particular military purposes which did not coincide with the requirements of commercial traffic and were not served by the existing highways. Few western imports have been found, and only five Latin inscriptions, three dedications by Roman soldiers and two milestones, have come to light in Iraq; it is significant that there is no known inscription of this period in Greek, the koinē of civilian life in the other provinces of the Roman East. Roman historians usually refer to Mesopotamia only as the scene of eastern campaigns of which they had, with the exception of Ammianus Marcellinus in the fourth century, no personal or detailed knowledge.